Clyde Shelton (Gerard Butler) is a talented engineer and family man whose life is ruined when two thugs break into his house, which results in the death of his wife and child in front of his very eyes.When the thug who commits the murders gets off with what amounts to a slap on the wrist by testifying against his less guilty accomplice (who gets put to death), Shelton initiates an increasingly elaborate plot to destroy the justice system.The prosecutor who made the agreement with the thug is the main target of Shelton, so he has to find a way to stop him before it is too late.
Black and Gray Morality: Let's see. He's a Well-Intentioned Extremist, willing to kill anyone to make his rather simplistic political statements. They're the forces of justice, who start out incompetent and unable to put away the bad guys, and wind up violating civil rights at the drop of a hat and staging vigilante executions.
Blatant Lies: Despite the Title Drop by Clyde, the only citizens never shown violating the law are the somewhat minor characters who get killed for making a crappy bargain that Clyde understandably feels is a mockery of justice.
Exact Words: Clyde, to Darby: "I want to keep you out of prison." He didn't say what he wanted to do to him instead.
Also in Clyde's first interrogation, he's very careful not to give Nick a confession.
Forced To Watch: Darby to Shelton, although he probably wasn't intending it.
Shelton actually ends up to doing this to Darby with himself.
Forgot About His Powers: Clyde — ordinary suburban homeowner, described as "a tinkerer", but turns out to be a genius in defence and violence whose abilities border on the fantastic. But he didn't bother to protect his own home from an intruder with a baseball bat. And why? Because he works best when he has prep time, not when he's surprised by said thug.
Whether intentionally or not, It's basically a movie about a Super Villain who suffered great personal tragedy and is now trying to bring down the justice system that failed him. There's no superheroes, no setpieces, and his plan ultimately fails thanks to Nick figuring the last bomb's location out. And he only was able to do that because Clyde accidentally killed Nick's assistant, whose boyfriend happened to have access to the right information, but wasn't willing to risk his job. Until his girlfriend, ostensibly just a woman who got Stuffed into the Fridge, was killed by Clyde.
Hoist by His Own Petard: Clyde is warned not to remotely activate his last bomb. He does so anyway, only to realize it was moved to under his seat.
Hollywood Law: Ames must have had one bad defense attorney if he's put to death purely on the say-so of his partner, on the question of which one of them was a murderer, a partner who is implied to have a much longer and nastier criminal record to boot. Apparently he never thought to call the husband as a witness either. And the prosecution are the only ones who even remotely care about his opinion as well, and still dismiss it.
The reason he's sentenced and his partner is effectively let off is a piece of evidence was contaminated by a CSU during the investigation, and all the admissible evidence is suppressed under Fruit of the Poisonous Tree doctrine. The problem with this is, Fruit of the Poisnous Tree only applies to evidence collected through rights violations, and more often than not it only applies to any confession made by the defendant. A piece of evidence contaminated during investigation of the crimescene isn't applicable.
Hypocritical Humor: Nick keeps leaving his cell phone on while in court with a certain judge. While in a meeting with her later, her cell rings, and he calls her on it. Turns out there's a bomb in the phone.
Idiot Ball: Clyde's non-confession would have been harder to pull off if Nick had announced something along the lines of "For the record, he just nodded his head".
Joker Immunity: A major point of the movie - the legal system is tied up in tons of red tape and thus no matter what they do they can't get rid of Shelton or even move him somewhere secure, so he is continually able to commit murders with relative impunity.
Karmic Death: Darby gets dismembered alive by Shelton, who recites the same line that Darby did before he committed the murders.
One judge scolds Nick repeatedly for not turning off his cell phone. She was killed by a bomb in her cell phone, which she hypocritically answered during a meeting with Nick.
Laser-Guided Karma: Less than 10 seconds after displaying flagrant contempt for duty, the rules and even the Constitution itself a bomb goes off directly in the judge's ear.
Might As Well Not Be In Prison At All: Clyde still commits murders, even in jail. Turns out getting sent to solitary confinement was part of his plan, since part of the preparations he made before getting arrested included digging a secret tunnel accessible from there.
Oh Crap: Clyde's reaction to the revelation that the bomb had been moved to his cell.
Averted seconds later, when he resigns himself to his fate, and utterly keeps his calm even with super napalm filling his cell.
Product Placement: Nick's understudy uses a Mac (apparently running Windows), and in one scene the staff prominently rolls in large amounts of Pepsi and Dunkin' Donuts. Every car is a Chevrolet.
Pun-Based Title: The dash is missing from "Law-Abiding" to show that it's the law abiding the citizen, not the other way around.
Red Herring: Nick's understudy is a minor one - around the time Clyde starts amping up his attacks she starts questioning Nick about whether or not he's in the right, and around the time they start questioning whether he has an accomplice inside their system we learn more about her mysterious boyfriend who never shows his face and "isn't ready" to meet Nick - the audience is briefly led to believe that she may be working with Shelton, and the boyfriend stuff was just another trick of his. When she dies, that part of the audience who believed that may even think Shelton pulled a You Have Outlived Your Usefulness on her. By the end of the movie, however, her boyfriend does appear, over the internet to give crucial information.
Roger Ebert also thought this about Colm Meaney's character.
Spanner in the Works: Clyde kills Nick's staff, including his blonde understudy. Said blonde's boyfriend happened to have access to critical information that he wasn't willing to risk his job over...until his girlfriend was killed.
Strawman Political: Although it shows up the dark side of vigilantism, the movie strongly suggests that the justice system is incapable of dealing with violent criminals, and "proves" this with some questionable logic;
"Plea bargains are bad, because here are some arbitrarily bad plea bargains for no adequately explained reason."
"The exclusionary rule is bad, because it got DNA evidence deemed inadmissible when there was no explanation as to what was illegal about how it was obtained."
To the Pain: Clyde goes into great detail about everything he's doing and is about to do to Darby.
Trailers Always Spoil: Clyde's past as a government weapon designer and "executive action" mastermind isn't revealed for over half the movie. The reveal itself is in the trailer, along with the Judge's execution, the mass car bombing, the drone attack in the cemetery and Clyde's napalm-induced end.
Villain Protagonist: Clyde is briefly alluded to be this in the trailer and the movie when the camera follows him up to the murder of Darby. The movie's actual protagonist turns out to be Nick.
Villains Never Lie: Clyde usually upholds his end of bargains (as long as the other side complies down to the minute), gives hints as to what he's going to do, and confesses when he's ready to. It's conspicuously averted when he tells the judge he's a law-abiding citizen, though (in other words, he tells the truth everywhere except in court). He also falsely tells Darby that he tazed a male cop.
What Could Have Been: Originally Gerard Butler was supposed to be Nick while Jamie Foxx was signed to play Clyde. At the last minute, though, Gerard thought it would be interesting to play Clyde, and asked Jamie if he minded switching roles. Jamie loved Gerard's performance in 300, and thought that as a viewer he would love seeing Gerard "beating people and blowing stuff up". Butler said that having Foxx and himself switch roles would be "awesome".
What the Hell, Hero?: The entire point of the movie. Clyde thinks he's doing this to the entire Justice system, and Nick keeps calling him out on it.
"Fuck [my] Civil Rights." Everyone in the courtroom is looking at Clyde like he's crazy.
Woobie, Destroyer of Worlds: Clyde eventually tries to destroy the entire justice department of Philadelphia, because they failed to properly punish the slayers of his family.