In Die Hard 2, terrorists infiltrate the airport baggage plant. They were wearing plain clothes, with no security passes. The doors weren't locked even back in the 70's they had key passes and CTTV cameras insenstive areas). John McClane and the terrorists engage in a shootout, which doesn't seem to alert security.
Harold & Kumar Escape from Guantanamo Bay: Kumar sneaks drugs and paraphernalia on to an INTERNATIONAL fight to Amsterdam. Kumar was able to bypass security by Causing a reverse racism scene where he accused a black TSA worker of racial profiling over Kumar's ethnicity. In reality this wouldn't work, as bags are placed on an x-ray convyer belt and questionable material are flagged and hand screened. Electronic devices are thoroughly checked for operational, even lighters are confiscated. Since Kumar carried a suspicious looking tube like object. The TSA could take him aside and further examine his baggage this policy extends to ALL travelers through modern airlines. Yet Kumar's threats to invoke the American Civil Liberties Union managed to cow and frighten "Mathew Perry" the security screener. Also when passengers get agitated, all they have to do is simply hit security. As sadly with the case of the RCMP officer tasering an agitated Polish passenger to death who was throwing chairs violently after being detained by flight delay.
The 6th Day, like The Simpsons, combines this with For Inconvenience, Press "1". The system's voice-activated, and the answer to each question is an increasingly annoyed "Yes." The last straw is when answering that there's a direct and current threat to someone's safety still doesn't connect the hero to a human being.
In Air Force One, the President's Secret Service detail and the armed soldier holding the nuclear football are all killed without so much as wounding a single terrorist. Is slightly justified in that the terrorists are all wearing body armor and armed with heavier weapons while the Secret Service has nothing but pistols. Also justified in that the guy heading the Secret Service is in league with the terrorists.
Played straight in most Alfred Hitchcock films, due to his own fear of the police from a traumatic childhood experience. However, it's subverted in Dial M for Murder, with a cop that works against the innocent framed protagonist but eventually figures out what's really going on and sets up a trap for the villain and Frenzy, where the cop suspects the protagonist's innocence right from the start.
Generally averted in The Amazing Spider-Man where Captain Stacey and the NYPD are competent when dealing with the Lizard and Spider-Man. After finding out that Dr Conners is a danger to the city, Peter's first reaction is to tell Captain Stacey about it. First thing Captain Stacey does is mock him and have a cop escort Peter out. The second thing is get another cop to investigate Dr Conners to see if Peter's concerns are justified.
When chasing Spider-Man, they do so by having dozens of snipers and a few helicopters firing non-lethal weapons, then completely surround Spider-Man when he's on the ground and quickly handcuff him while he's barely conscious. Spider-Man is released by Captain Stacey when its clear that he's the only one that could stop the Lizard and protect Gwen who was in danger.
Angels & Demons has a really bad case of this. Although this was supposed to be a more or less rational thriller, a single assassin manages to kill the Italian and Papal police presence at a top-priority crime scene in city centre of Rome, using little more than a Silencer Pistol.
Shortly after, Langdon manages to convince two Carabinieris to accompany him to the soon-to-be crime scene to stop the killer in time. The van with the assassin and the next victim arrives boldly. The policemen, however, (instead of, you know, calling for better armed reinforcement, seeing how he had managed to kill a dozen others earlier), immediately try to sneak around the van, one by one (not even attempting to sneak in or something). They also are eventually sniped by the killer one by one, who then proceeds pushing his fourth victim into the water unhindered.
Later in the movie, Langdon and the Italian special units storm the presumed criminal hideout. But instead of following Langdon's directions like they were supposed to, they run off into the other direction for no obvious reason, even though Langdon begs them to stay with him. A few minutes later, he finds himself face-to-face with the armed assassin.
And The Da Vinci Code (the predecessing film), actually shows the police to be partially competent rather than completely incompetent. The French police, for instance, may not have managed to catch Langdon and his cronies, but still managed not only not to leave them unguarded in the Louvre, but also to seal off the American embassy and all the public Transit of Paris, and managed to track them down very fast over and over, by investigating in the right spots, and asking the right people.
Langdon only managed to escape the first time due to an insider helping him, the second time, because a bank director hijacks one of his own armoured money transporters, in which he hides Langdon and Neveau (and convinces the police, that it can only be opened again upon reaching it's destination, Geneva), and the third time, because Teabing and his butler drive them from their property in a badass crashcourse through an off-track rough forest in their Land Rover, before the police manages to storm the Chateau.
The police in Britain are equally competent. They fail to stop the plane on the airfield, and Langdon manages to get out before the police catches up with the halting plane. Yet, they did manage to dispatch Silas and Aringarosa and to find Teabing, Langdon and Neveau, partially using investigation (but paying with a few injured police officers during the raid of Opus Dei House).
Played for Laughs in The Big Lebowski. When asked about leads regarding the Dude's stolen car, the policeman replies ironically: "Leads, yeah, sure. I'll just check with the boys down at the crime lab, they've got four more detectives working on the case. They got us working in shifts!" This is actually Truth in Television as the car itself has almost no value and therefore they really wouldn't care all that much. Auto theft isn't generally a huge priority anyway.
The Blob, starring Steve McQueen, is perhaps the archetypal example. Which is odd because it actually plays against itself throughout with one cop willing to trust the teenagers and another (the former's subordinate) being extremely distrustful of them.
Subverted in Blue Velvet, where Jeffrey actually does consult a police detective and knows that he should just leave things to the police but keeps investigating on his own anyway. Admittedly, Dorothy Vallens repeatedly tells Jeffrey "no police" when he tries to help her, but it turns out she has good reason to be afraid- Det. Williams' partner is in league with Frank Booth.
The "party cop" from Cabin Fever. Instead of doing his job and helping the protagonists, he's only interested in partying. And talking about partying.
Changeling. First, the police (who, in that area, were extremely corrupt at that time) refuse to investigate Walter's disappearance until the morning after Walter's mother Christine reports it. Then, after months of searching, they give her a boy who isn't her son. They refuse to believe her when she points this out, despite many obvious discrepancies between his physical characteristics and Walter's (such as the boy being three inches shorter than Walter). It just keeps getting worse from there, with the police actively obstructing any and all attempts to locate the real Walter, simply to avoid losing face. An officer who has discovered a possible murder case is even ordered not to investigate because it could mean finding the real Walter's body and admitting that they never found Walter to begin with. They even go so far as to have Christine involuntarily committed to a mental institution to destroy her credibility. The staff there turn out to be no less corrupt than the police. The worst part is that Changeling is based on a true story.
The police are depicted as being extremely incompetent in The Chaser, to the point where they're more concerned with damage control over someone throwing shit at the mayor than they are with a missing woman and a man who confesses to be a serial killer and claims that he's holding her captive.
Lampshaded in Color of Night by Capa when Detective Martinez shows up just after he was almost bitten by a rattlesnake planted in his mailbox.
Just like a cop! Never there when you need them!
A somewhat more well-thought out example happens in Demolition Man. The San Angeles Police Department has been reduced to a peace-keeping force for a city full of petty crimes. As such, when Simon Phoenix, a real criminal awakened from cryogenic stasis, starts making trouble, the police are utterly incapable of stopping him. Only Spartan, a cop from the same era, is up to the challenge.
While reporting a ghost is pretty ridiculous, it's hard not to shake your head when the police officers in Dead Friend laugh in Ji-won's face and call her crazy when there are a bunch of random, unexplainable and downright impossible deaths happening around the city.
In Live Free or Die Hard, this is subverted due to the police being rendered incapacitated by Gabriel's cyberterrorist attack (blocking cell phone signals and causing gridlock on highways).
Showcased in the idiotic Jennifer Lopez movie Enough. As one review put it, "I wonder how exactly the judge would word his ruling. 'While it is true that your husband has beaten you and that you have produced three separate and unrelated groups of reputable witnesses from around the country who say that he has committed at least a dozen serious felonies, including threatening to murder six different people, the mother of his child among them, I rule that custody goes to the father and furthermore proclaim that he shall not be prosecuted for these crimes because he is rich. Even though J-Lo is now rich too, via her father. I just hate women. And children. Bwoohahahahahaha'"
Ferris Bueller's Day Off: The police don't believe Ferris' sister when she calls them about Principal Rooney breaking into her house.
It's worse than that. It takes her several minutes to finally convince the police to show up, and it likely takes several more for them to get to the house, and when they finally do, they immediately turn around and arrest her for making a fake call, there being no intruder present. Because, after all, if an intruder is found out, it's not like they'lltry to leave the area or anything.
She even had evidence; the intruder went and left his wallet in the house.
Four Lions just might represent the high point of cinematic police ineptitude. Not only do they fail to stop a suicide attack (and arrest the wrong guy when they get wind of it): They arguably cause more mayhem than the terrorists they were trying to stop.
The sheriff in Frailty automatically assumes that Fenton is lying when he comes and tells him in a total panic that his father has murdered at least two people and immediately has a sit-down with his father as the first course of action. Then again, the movie's such a Mind Screw, so it's hard to tell how much, if any of the story told is true or not.
In Friday the 13th Part VI: Jason Lives, Tommy Jarvis desperately attempts to warn the police of Crystal Lake/Forest Green after he accidentally brings Serial Killer Jason Voorhees back to life, but nobody but the sheriff's own daughter will believe him. Jason's subsequent bloodbath only convinces the cops that Tommy himself is the killer, acting out a delusion of Jason's return. Never mind that the sheriff's daughter can vouch for Tommy because he was with her during two of the murders. The cops are only forced to accept Tommy's story when they are attacked by Jason himself at the camp, and promptly killed.
On the other hand, when a kid who spent several years in the institution and is under psychiatric care shows up and claims a notorious murderer, who is dead and buried for years, was revived by a lightning and is now a zombie, prowling around with a machete and killing people, would you believe him unconditionally? Actually, the sheriff's daughter is the one who's behaving irrationally here.
Subverted at the beginning of Jason Goes to Hell: The Final Friday. The FBI spring a trap on Jason and actually take him seriously, attacking him with a small army's worth of firepower and an airstrike, managing to actually blow him to bits. It doesn't keep him down, but it was a very impressive effort.
Played straight with the Chicago Police Department. They suspect and arrest Richard Kimble for his wife's murder within hours and don't appear to do any investigating into his (truthful) account of what happened, whereas Kimble, once he escapes, is able to track down his wife's killer within weeks. To make matters worse, the guy is a former Chicago cop, resulting in the Unfortunate Implications of the department deliberately letting an innocent man take the rap in order to let one of their own walk.
Averted with Gerard and his team of US Marshals. Although technically incorrect in their pursuit of Kimble, they are not the least bit incompetent, and end up being his allies in proving his innocence.
The remake of Fun With Dick And Jane had one part where a Latino man impersonates Dick with a picture ID. And it works.
In Gremlins, Billy's efforts to warn the police about the title creatures get blown off. But hey, would YOU have believed him? It gets even worse when those same cops see a man being mauled by the creatures and they don't bother to help him.
A MAD spoof of the film makes fun of this. A cop tells Billy, "The police never listen to the hero until it's too late!" Then he mentions films like The Blob.
Billy suffers similar disbelief and a helping of mockery from the security team in the sequel. They wise up when one gremlin tears through their surveillance system and assaults them.
Also played straight, since earlier in the movie Michael single-handedly slaughtered the Haddonfield police force. There's a reason the state police were called in.
In Rob Zombie's Halloween II (2009), Sheriff Brackett asks Andy, one of his deputies, to protect Annie. To say he fails horribly shouldn't come as a shock.
The cops in The Hangover, both movies are pretty useless. In the second movie, the cop at the desk is merely extremely apathetic to the guy's problem of Teddy being missing, simply giving them a monk who has Teddy's clothes and ID and dismissing it as not being his problem from there. The cops in the first movie, however, are pretty extreme in ways that screw everybody. First, they arrest the guys for stuff they did last night, fair enough, they did break some laws. Then they more or less refuse to help them with Doug being missing. Then they show uselessness in a way that helps the protagonists, but simultaneously screws them over, as they allow them to escape their arrest with no charges in exchange for being tased, something all officers involved are clearly getting a huge thrill out of doing.
Subverted in Hocus Pocus. The apparent cop who bullies the children begging for help (insulting Max's manhood) is only a man in costume on Halloween. It plays Adults Are Useless straight, though.
The cops in Home Alone are poster children for this trope. When Kevin's mother calls them to report that her eight-year-old son has been stranded alone for at least a day, she spends several minutes being bounced around between two bored cops who can't be bothered to try to comprehend what she's telling them before finding someone else to foist her on. Eventually, they dispatch a third cop, who then waits all of 45 seconds after knocking on the door of Kevin's house before concluding that no one is home and leaving.
Slightly more justified in Home Alone 3. The cops show up the first two times Alex calls about a burglar. However, since the bad guys are internationally-wanted criminals working for North Korea, not run-of-the-mill crooks, they are able to evade detection and capture (although the cops appear to lack peripheral vision). He doesn't call them a third time, thinking they wouldn't show up. He does, however, call an Army recruiting office about a strange computer chip he finds in his toy car. While the sergeant dismisses his claims, he does agree to pass the serial number up the chain. He does, and it eventually reaches the office of the Federal agent looking for it, who immediately heads to Chicago.
Hot Fuzz: Although Nicholas Angel himself is an obvious subversion, the central device allowing the plan of the bad guys in the movie to work is based around the idea that the Sanford Police Force are a bunch of incompetents who've been lulled into such a false sense of security and complacency by the tranquility of the village that they will respond to even blatantly obvious acts of homicide with the assumption that it's an accident of some kind. And they do, to the extent that their complete inability to recognize the blindingly obvious at one point leads Nicholas to doubt his own sanity. Ultimately subverted, however; once their eyes are truly opened to what's really going on in their village, they transform almost immediately into an efficient, competent unit more than capable of kicking ass and taking names.
Partly justified because the police chief is in on the conspiracy, and deliberately trying to keep all the other cops complacent.
Also London's police department. They throw Nicholas out for making the rest of them look bad, and then beg him to come back in the end, when they realize that the crime rates are going up in his absence.
An extremely sad example of Truth in Television is depicted in Hotel Rwanda. During the 1994 Rwandan genocide, the United Nations soldiers stationed in Rwanda were not allowed to shoot the militiamen who were slaughtering Tutsis all across the country. Most of the native Hutu police took part in the genocide themselves. Within less than two months, over one million civilians were killed.
Jack: I'm only allowed to leave four soldiers stationed here, Paul. And they're not allowed to shoot.
To a completely idiotic degree in Identity Thief where the cops don't do anything at all to stop an identity thief from Miami despite knowing where that criminal will be, they don't even make a phone call to MPD or the Feds at all by handwaving it with Hollywood Law. They even let the Jason Bateman character to kidnap the criminal, essentially having do their jobs.
The cops in Intruder on two instances. First is when they come to check a disturbance caused by one the workers' ex-boyfriend and then quickly leave without putting any effort on finding him and second is in the end where they arrest the wrong people for the killings.
Many James Bond films, particularly (for some reason) the ones with sequences in America, see Bond having to avoid getting arrested by the police as well as staying on the villain's trail. Luckily, they're all hopeless drivers.
This actually makes perfect sense, since what Bond is doing actually is illegal. Most of the movies, after all, take place on foreign soil, where Bond has no legal powers whatsoever and would doubtless be arrested as the spy he is if the cops found out what he was doing.
With the U.S., it's a gray area-in some cases he's working with Leitner and the CIA and his actions are sanctioned, in others (like Licence to Kill) he's operating without authorization.
Averted in the horror movie Jeepers Creepers. When the two frightened, teenage heroes from out of town run to the small-town police in the middle of the night with wild stories about a monster pursuing them, the police utterly break the formula by being quick to believe them and trying their level best to protect them, with the force finally facing down the monster in a standoff. Their efforts prove useless, though, as it has a Healing Factor.
Not necessarily. They just needed more men and larger guns: when they showed up at the end in full body armor and armed with assault rifles, they force the thing to flee. It was quite obviously worried about being killed at that point.
Played for Laughs in the Jurassic Park sequel The Lost World. While running wild through the streets of San Diego, a Tyrannosaurus Rex is confronted by a fleet of police cruisers. The dinosaur roars a challenge, and all the police cars promptly turn around and take off, leaving the city and its civilians to fend for themselves.
In Killer Klowns from Outer Space, Sgt. Mooney doesn't just ignore the protagonists — he gets dozens of calls from citizens under attack, and declares all of them to be pranks... and ends up an Asshole Victim for it. On the other hand, his direct superior does believe the kids, when given enough evidence, and ends up displacing the protagonist as the film's real hero.
In The Last House on the Left, the sheriff and his deputy are incompetent buffoons. They even buy into Krug's half-assed alibi about being a passing preacher. And when they hear of Mari's kidnapping, they not only find out where she is located, but also that they were there a few minutes ago. Oh, and they were late to the Roaring Rampage of Revenge Party.
The Lifetime Movie of the Week, A Cry For Help, doesn't even begin to describe this trope. First off, the abusive husband already has a restraining order against him, but it doesn't stop him from marching on over to Tracy's house. Then Tracy calls the cops, who take their sweet ass time getting there. By the time they do, the husband has stabbed her multiple times. This also draws in a crowd, who now are witnesses to this crime. The cop also restrained a guy who was restraining the husband, who beats her up. Guess what the cop does? He stands there and looks as the husband beats her up and rants on how she should die. While they did call an ambulance and restrain the husband from clawing at her while she was on the stretcher, the fact that they could have done so much more and could have prevented some of the damage done onto Tracey got them sued for it, makingthis... For reference, this is based on a true story, and the resulting lawsuit considerably improved the average police response to domestic disturbances.
"Manos" The Hands of Fate may be one of the most credibility-stretching examples. The police, who spend most their time harassing a young couple at Make-Out Point, finally hear a gunshot fired by the protagonists, who are being chased through the desert by an insane cult. The cops don't get four feet away from their car before giving up and deciding that the gun was probably fired somewhere in Mexico and that it doesn't concern them.
"Sound does travel a long way at night."
In the B-movie pastiche Monster, the Genre Savvy mentor instructs his successor that the police will never show up until after the monster is defeated. In the end, after The Hero dunks the monster in a vat of liquid nitrogen, he wonders where the cops are and realizes that it must still be alive. After defeating it one more time, the cops finally show up.
Averted in The Monster Squad when the character Eugene writes a childish letter to the military about Dracula; they actually show up at the end. And again with Sean's dad, a cop, who immediately gets on board to help his son once he figures out what's going on.
Also the schtick of The Naked Gun movies for the most part. Lt.Drebin does get his man in the end, but getting there is a comedy of errors.
Big time in Neighbors. They don't respond to a noise complaint and the responding officer actually warns the frat that they got a complaint. Though it is at least partly the fault of the Radners as they lie outright about making an anonymous complaint and then immediately get caught in another lie about partying with the frat the previous evening.
No Country for Old Men has an ideal example of the police doing absolutely nothing useful whatsoever for the course of the film. They might has well have never been there, including the star sheriff played by Tommy Lee Jones. The worst example has to be when they first visit Llewyn's trailer, which turns out to be empty, but someone has clearly been there due to the milk being left out and cold. The sheriff dismisses the idea of mentioning that the murderous psychopath Anton Chigurh is around, due to them knowing nothing about him—it doesn't occur to him that others in the park might have seen him, most notably, the person who directly interacted with him, the owner of the park, as well as any others who probably noticed him breaking into Llewyn's trailer. Later in the film, Sheriff Bell learns that Llewyn is headed to El Paso, and promises Llewyn's wife only he will go to see him...which is at least six hours from where he is at the time. Sheriff Bell does not alert the El Paso police that there might be a massacre exactly there, nor does he seem too concerned about the fact that it's probably safe to say Anton will be there, too. The obvious happens when a simple phone call to the El Paso authorities saying a massive gun battle was about to break out there would have given them some cause for concern. Instead, he lets all of it happen without telling anyone about the inevitable shootout that's definitely going to occur before he gets there.
The Other Guys both parodies and plays this straight, then again they play it so straight it might also be parody. The chief repeatedly shuts the guys' investigation down and ignores all of the evidence they're getting because he told them not to investigate anymore. Subverted because Da Chief actually does know full well that there is something going on. In fact, he just wants to keep the two titular guys away from the danger zone (he is probably the most timorous Chief you'll ever see in modern media). In the end, they actually convince him to help them for a change and to support them in their pursuit. He does.
Pain and Gain: The Miami police write Kershaw's story off as "delusional alcoholism" and don't do anything about it. Even after Ed Du Bois presents a lot of evidence to them, they don't take any action because they're afraid it would make them look bad for ignoring Kershaw before. It isn't until after the Sun Gym gang claims 2 more victims that the police try to arrest them. Then averted when they finally take action, as they're able to apprehend the gang in short order without a lot of trouble.
Played with in Jodie Foster's movie Panic Room, the protagonist calls 911 only to be put on hold. When the police do finally show up, it's because her worried ex husband called them. And still the cops are dissuaded from sticking around, though that's only because she is the one to tell them it was a false alarm, and one of the officers suspects (correctly) that she is under duress.
Subverted in Pineapple Express. The heroes avoid going to the police because one of the villains is a cop. When Seth Rogen gets arrested, he finally spills his guts to the arresting officer, who immediately believes his implausible story and vows to crack the case. After getting "rescued" from the cop, Rogen berates his friend for ruining everything.
The premise of the Police Academy movies. Somewhat subverted though, as the bad guys are even more incompetent.
The opening sequence of Predator 2 had the LAPD having a gunfight with a much smaller group of Colombian drug dealers and the police were the ones who were defeated. Justified because the drug gang had better weapons, including grenade launchers, while the police were limited to pistols and shotguns. They were also holed up in a better position. And what's worse, the SWAT-team wasn't available because they were already engaged in a similar situation elsewhere.
Taken to ludicrous extremes in the Prom Night (2008) remake: a police department cannot prevent a former high school teacher armed only with a knife from murdering several people despite knowing exactly where he's going. He also manages to evade them all... by putting on a cap.
The Purge: Justified Trope. One of the rules behind The Purge is that the police cannot respond to any calls for 12 hours. As a result, if you get into trouble, you're on your own.
Subverted in the Die Hard-on-a-bus film Speed where the police are actually competent at helping out the protagonist, forming an escort to prevent collisions, mapping out a survivable route with the help of a police captain from a chopper and blocking off roads so the bus won't explode. It helps that the protagonist is another cop, but that just goes towards subversion, too. The S.W.A.T. officers provide the exception; they try to assist the woman off the bus while on the highway, despite knowing that the killer is watching and told them explicitly not to do that.
In Spider-Man 2 the titular hero's 10-Minute Retirement caused the crime rate in NY to skyrocket by astounding 75%. That's right. One man, albeit a superpowered one, managed to contain almost as much crime activity as the whole NYPD did. Like Batman before him it was more the knowledge that Spider-Man was out there that kept most of the lower-level criminals at home, leaving only guys like the Green Goblin and Doc Oc to take over. Once word gets out that Spidey is gone (thank-you, Mr. Jameson) they come out of the woodwork and crime skyrockets, with the press inflating the figures to sell more papers.
In Superbad the two cops are a good deal less mature than the teenage protagonists.
In the French film franchise Taxi, the police forces of Marseille are completely incompetent except for Petra. It says a lot about their boss' abilities that in the third installment he talked about his brother, who copied one part of the exam wrong from him, got zero points and thus couldn't become a police officer.
The first movie plays the trope differently: Most of the cops except Emilien are decent enough, they are just outside the area of expertise to catch those particular crooks. The chief is peculiar... but not outright incompetent, the implication being that the pressure of this crime wave is getting to him. The sequels make the cops outright dumb and dangerous: Only Petra is in any way competent, and the cops are more dangerous to the city than the criminals themselves.
In the fourth film, Petra and the French Intelligence stage a Batman Gambit using the cops' incompetence.
Thompson and Thomson in the Tintin movie. One man they talk to gets nervous at mentions of the pickpocket they are looking for, evidently doesn't want police officers in his apartment, and when they are inside, they find dozens of wallets on the shelves. He claims he is a wallet collector and they believe him.
In Trick 'r Treat, when Mr. Kreeg is being menaced by the evil spirit Sam, he calls 911...and is immediately put on hold. Sam then cuts the line, and no patrol cars or other emergency response are ever dispatched to the location of the call to check up.
In WarGames the FBI is sure that Lightman is a criminal:
Nigan: He does fit the profile perfectly. He's intelligent, but an under-achiever; alienated from his parents; has few friends. Classic case for recruitment by the Soviets.
In all fairness, he did hack into a national defense computer & immediately fired up the ICBM software. You can understand the mistake.
Booking getaway tickets to Europe would also be a clear warning sign.
Scream: This is zig-zagged; during the finale of the first film, the only cop present - Dewey - is taken out very quickly, and it's Sidney and Gail that put an end to everything. In the second, the police hold a single press conference, and only show up again at the end after everything has been settled. By Sidney and Gail again. In the third film, police are more prevalent, but again, the only cop on the scene is taken out rather quickly, and Sidney, Gail and Dewey (no longer a cop) deal with it. During the fourth, the police have a strong presence (most likely due to being under Dewey's command, given he's dealt with this several times before) but are nowhere to be seen when several deaths occur. The Zagging comes in when you consider that despite their efforts usually accounting for nothing much, the police actually do actively try to help the protagonists, for example, imposing curfews, posting bodyguards to Sidney (and by proxy, those around her) and usually believing the protagonists almost immediately when it becomes apparent that they're being targeted.
Zodiac deconstructs this trope pretty well. It's not that the SFPD are incompetent, per se - by the movie's account anyway, Detective Toschi fingers the correct suspect early on and arrests him at one point. However, a number of contributing factors hamper his investigation: overlapping jurisdictions among different departments, the lack of hard evidence, adverse media coverage, a panicky public, and just plain bad luck.
In Commando, the police who arrest Matrix at the army surplus store don't even bother to put Matrix in cuffs, and they also fail to notice that Cindy is helping him. They also dismiss Matrix's requests of trying to get in touch with General Kirby as crazy talk, not to mention that when they finally do notice Cindy, they mistake her as a prostitute.
Also in an earlier scene at the mall, they all piled up on Matrix even though Sully killed several of the cops left and right. Though somewhat subverted that a cop manages to take out Sully's money man.
National Security: After spending 6 months in jail, former cop Hank Rafferty discovers that, in his absence, the investigation into the warehouse break-in, during which his partner was killed, hasn't moved an inch. Hank and Earl end up breaking the case wide open in a few days. Slightly justified because Detective McDuff, whose case it is, is actually working with the criminals. The other aspect is that the LAPD seems more willing to throw one of its own to the wolves rather than risk a riot in the city over something that has, at best, questionable evidence.