The Unsolved Mystery - Television Tropes & Idioms

Kellerman: Enough with the metaphors.
Munch: If not metaphors, what are we left with? We have a riddle, surrounded by a mystery, wrapped inside an enigma, and stuffed inside a body bag.

— Homicide: Life on the Street, "Shaggy Dog, City Goat"

In Mystery Fiction, the most common ending is the one where the mystery is solved. The detective figures out who the murderer is, the mask is pulled away, the villain shouts "And I would have gotten away with it too if it wasn't for You Meddling Kids," loose ends are tied up, and everyone (except the villain, of course) goes home happy.

Not so with some cases. In some cases, there are no answers. In some cases, the detective doesn't even know the right questions. This isn't just a Karma Houdini, where the bad guy gets away without consequences. This is where the characters don't even know who the bad guy is or where to start looking or perhaps what the hell just happened.

Examples:

Comic Book

During the time between Zero Hour and Infinite Crisis, the mystery of who killed Thomas and Martha Wayne had actually been this, part of a number of sweeping changes editor Dennis O'Neil wanted for Batman.

Film

The Pledge: the case is never solved and there are no details on the murderer except that he's a tall man and he died in a car crash approximately 15 minutes before the hero could learn his identity and catch him. Tough luck.
The Mothman Prophecies.
Memories Of Murder, based on the Hwaseong serial murders of Korea.
In Minority Report, John Anderton never finds out what happened to his missing son.
Black Death in which a group of soldiers are sent out in order to investigate an idyllic village that seems to have been spared from the pestilence. Pretty much everything that they see in the village, whether it be a resurrected girl, a woman with supernatural powers, or the lack of disease, could have a rational explanation, or could in fact be the work of demonic powers. No one ever finds out.
The homicide case in Zodiac remains unsolved.
In The White Ribbon we never learn who committed the crimes.
The Thing (1982). One of the main mysteries of the film is who, exactly, sabotaged the blood samples kept in storage. Early on, they narrow it down to either Gerry or Dr. Copper, neither of whom turn out to be The Thing. The other mystery is whether or not Childs became a Thing when he went missing shortly before the confrontation with Blair. The film ends with MacReady and Childs resigning to death from the arctic cold, both of them unsure if the other is human.
Bullitt. The Cowboy Cop kills a key witness whom he was supposed to bring in alive, so they never find out who is behind the organized crime operation. Movie over.
In the film, Picnic at Hanging Rock, we never learn how or why the girls vanished. The novel did have a chapter that explained it but the publishers decided to keep it a mystery in most editions.

Literature

The Sherlock Holmes story "The Five Orange Pips", from The Adventures of Sherlock Holmes. Though Holmes is certain that the murderers, high-level members of The Klan, are on a specific ship, said ship apparently sinks at sea, and their identities are never determined.
- The Problem of Thor Bridge states that there were problems even Sherlock Holmes couldn't solve, but they were not published by Doctor Watson because the audience would have felt cheated:
Some, and not the least interesting, were complete failures, and as such will hardly bear narrating, since no final explanation is forthcoming. A problem without a solution may interest the student, but can hardly fail to annoy the casual reader. Among these unfinished tales is that of Mr. James Phillimore, who, stepping back into his own house to get his umbrella, was never more seen in this world. No less remarkable is that of the cutter Alicia, which sailed one spring morning into a small patch of mist from where she never again emerged, nor was anything further ever heard of herself and her crew. A third case worthy of note is that of Isadora Persano, the well-known journalist and duellist, who was found stark staring mad with a match box in front of him which contained a remarkable worm said to be unknown to science.
In The Sherlockian, an obsessed Holmes fanatic kills himself after realizing that the lost Conan Doyle diary he's been seeking for most of his life had been destroyed. Unable to live with the prospect of never knowing what Doyle'd written in it, he stages his suicide to look like murder for his fellow-Sherlockians' benefit. Played with and double subverted when the Holmes fan who successfully investigates his death discovers the diary does still exist, but contains an admission that would seriously tarnish Doyle's (and therefore Holmes's) image. His companion destroys the diary, leaving Doyle's secret forever The Unsolved Mystery for the rest of fandom.
In another Sherlock Holmes example, Mitch Cullin's A Slight Trick of the Mind features an elderly Holmes dealing with three cases, two in the past and one in the present. Holmes solves two of them, but the third, the disappearance of Mr. Umezaki's father, completely stymies him: he cannot remember meeting Mr. Umezaki's father, despite evidence that he has done so, and has burned the volume of Watson's journal that probably would have allowed him to reconstruct the man's fate.
Frederick Forsythe's book The Day of the Jackal. The titular assassin is killed trying to carry out his plot against Charles de Gaulle, but his real identity remains unknown to the end.
The Colorado Kid by Stephen King. Two reporters tell their intern about the mystery of the Colorado Kid: a guy found dead on the island, even his name unknown until a year later. Not only is who or what killed him unknown, but nobody knows why he was on the island (he didn't live there) in the first place.
One of the The Cat Who books was like this. Not only do the characters not find out what happened or who killed the victim, the readers don't, either!
Played with in Vernor Vinge's Rainbows End: the main villain is revealed to the reader in the beginning of the book, but none of the characters figure out who it is. The trickster, on the other hand, might or might not be an AI and is only ever seen as a holographic rabbit - not even his name is known.
John Grisham's The Associate. In the end, Kyle McAvoy never learns who Bennie Wright really was, who he was working for or why he wanted the Trylon-Bartin documents. Kyle even points out that he couldn't have been Bennie's only spy at Scully & Pershing; Bennie had knowledge he could only have gotten from an inside contact, a partner no less.
This happens unintentionally in Raymond Chandler's The Big Sleep. One of the murders is never explained, and when it was pointed out to Chandler, he found himself surprised to realize that even he didn't know who had killed that victim.
- That's the legend, anyway. In fact, the novel does contain an accumulation of evidence pointing to a particular solution, it just lacks a concrete "yes, that's definitely the solution" moment.
The Nancy Drew story The Clue in the Old Album is kick-started when Nancy witnesses a man steal an old woman's purse during a concert. Nancy goes after him and manages to retrieve the stolen property, learning on its return that the woman didn't care about anything in her purse except several letters. From there the story veers off on a completely unrelated tangent, and though the woman remains a central character, no one ever learns what was in the letters, or why they were so important.
The Crying of Lot 49 combines this with Interrupted By The End, coming to a close mere seconds before the mystery is solved. Why? Because Thomas Pynchon enjoys messing with you.

Live-Action TV

The show Unsolved Mysteries, of course.
The Law & Order franchise has done this a few times, usually in the form of cutting to the credits right before the verdict in a controversial trial is read, or ending without revealing the outcome of a tough decision that the main character(s) or guest star is forced to make.
Done in the Cracker episode 'One Day A Leming Will Fly'. A teacher, in custody as a suspect, confesses to the murder of a school pupil, but then when he is alone with Fitz, tells him that he didn't do the murder but feels so guilty about his treatment of the boy (not to mention all the pressure the public, the police and especially Fitz put him under to "confess", lasting nearly two whole episodes) that he said he did it anyway. The real murderer is never identified, not even any plausible suspects are put forward. Worse, Fitz wasted so much time on this teacher, and the case has acquired such a high-profile, that his boss decides to ignore his pleas that he got it wrong and still try and convict the man for the crime.
The Adena Watson case on Homicide: Life on the Street. In fact, a lot of cases end up not being solved, since Homicide stuck very close to real life.
One Seinfeld episode had Jerry getting increasingly frustrated that his Girlfriend of the Week refused to taste a piece of apple pie and wouldn't tell him why. Despite many efforts, he never learns why she turned down the pie, declaring the mystery "one for the ages."
- Similarly, in "The Seven" Jerry's Girlfriend of the Week wore the same dress on all of their dates with George and Jerry trying to figure out why. This eventually drives him crazy and she dumps him before he can find out when she catches him starting to go through her clothes.
Jerry: What in God's name is going on here? Is she wearing the same thing over and over again? Or does she have a closet full of these, like Superman? I've got to unlock this mystery!
Farscape: who killed Salis in "Durka Returns"? Especially since one of the two main suspects is a regular character, and there's a common Epileptic Trees fanon that it was actually another of the regulars.
Doctor Who: What the hell was the Midnight Creature?
So many things about Twin Peaks. Namely, is MIKE a good guy or a bad guy? What about The Man From Another Place? What was the deal with The Log Lady? Who was that kid with the creamed corn? How is Annie?
- In fact, David Lynch initially intended the central mystery of the series - that of Laura's murder - to remain unsolved as well, but Executive Meddling forced him to change this.
- The movie, Fire Walk With Me, opens up even more questions. Why was David Bowie distorting the space-time continuum? What happened to the Chris Isaak character? Who was the Jurgen Prochnow character from Laura's dream? What was that monkey about, and who is this Judy person it mentions?
The Prisoner. Why did Number Six resign? We never know. Whose side was The Village on? We can only guess. Was Number One a clone? A twin? A hallucination?

Real Life

Truth in Television, unfortunately:
- Jack the Ripper.
- The Zodiac Killer.
- The Black Daliha.
- Hwaseong serial murders
The second colony of Roanoke Island. Established in 1587, one of the governors decided to return to England to gather supplies, since lack of supplies was why the first colony failed. War with Spain prevented him from returning for three years. When he finally did return, the colonists had all disappeared, with only the word "CROATOAN" carved on a fencepost as a clue to their fate. To this day, no one is sure what became of the colonists.
- Of course, there's the small matter of the native Croatoan tribe who lived on the other side of the bay, who, when they were finally investigated, turned out to have a surprising number of members with blond hair and white skin. Rendering this more of a Real Life Subverted Trope.
  - Or at least, that is one of the prevailing theories of what happened to them. Without DNA testing, there's really no way to know for sure, so it ends up being more a case of "Probably Solved Mystery But Without Proof We'll Never Know".
  - A similar case is the disappearance of Amelia Earhart. Several artifacts believed to come from her plane (and a possible skeleton, although the bones themselves are lost and there's considerable evidence both for and against) have been found on Gardner Island, close to her last planned refueling stop, but whether the plane landed there or the items washed onto shore after a crash at sea is unknown.
Jillian never found out why they weren't wearing pants.

Video Game

This is what happens if you don't get the True Ending in Persona 4.
- Specifically, this is what happens when you don't get the Good ending. The Bad one acts as the sad outcome, and the characters never ask themselves about the contradictions.
Silent Hill.
It's easy to go through the Laura Bow adventure games and have no idea what is going on. Even if you manage to get the good ending, it's possible you haven't figured out quite everything behind the mystery.
Either of the Dead Rising games if you ignore the main storyline.
An in-universe example. In Batman Arkham City, there is a sidequest named "Watcher in the Wings", about a mysterious stalker that Batman keeps seeing. When you finally confront him, he names himself Azrael talks in riddles about a prophecy involving Batman and Gotham City. Batman simply says "I don't believe in fairy tails" and Azrael leaves. Batman fans know who the guy is and have probably figured out what he's talking about, but Batman has no freakin clue about what that all was.

Web Original

Who killed Sherrif Deer in Sluggy Freelance.
Ruby Quest. A girl wakes up in a coffin in some mysterious place, frees this guy from his prison downstairs, and together they start to make their escape and try to find some answers, in that order. They do get away in the end, and many answers were found, but so very much was left to shadows as well.
- Justified, though, due to the nature of the game. Word Of God is that, had the players done a couple of things differently, more answers would have been uncovered. Notably, Filbert was supposed to explain a lot, but he ended up kind of, well, dead.