Chronic Evidence Retention Syndrome

Ladies and gentlemen, we'd like to raise your awareness of a tragic disorder affecting everyone from common street thugs to criminal masterminds everywhere, Chronic Evidence Retention Syndrome. Responsible for the downfall of many otherwise competent bad guys, CERS can be recognized by some of the following symptoms:
  1. The pointless hoarding of evidence against oneself even when there's absolutely no need to do so;
  2. Keeping easily destroyed or otherwise easily discarded evidence intact;
  3. Having said evidence in a location trivially linked to you; and
  4. In extreme cases, actually going out of the way to make sure it's clear that something is evidence, and linking it to you.

Please note that retaining evidence of a crime where the evidence consists of, say, something valuable you wanted to steal, isn't symptomatic. In a genuine case of CERS, the evidence will have absolutely no value to anyone other than proving the holder guilty. So be on alert for these symptoms, and so long as the criminal mastermind isn't the Shoot the Messenger type, let him know he may be making a critical mistake.

Generally a subtrope of someone simultaneously holding the Villain Ball and the Idiot Ball. Typically, one can expect the person to be a Smug Snake, thus making his eventual downfall all the more satisfying. If an underling does it, expect the Man Behind the Man to make sure he doesn't get a chance to do it twice.

Examples:

Comic Books
  • In both comic and movie versions of Watchmen, Veidt for some reason didn't erase the computer files that detailed his plan to frame Dr. Manhattan for causing cancer and leaving Earth, and information on his ultimate plan, even though the Manhattan plan had been successful (so far as he knew) and he'd already kicked off the second, so there was no need to keep the files at all.
    • It's possible that he wanted the files to be found so that his friends would confront him and thus leave New York at the time of its destruction. I mean, why else would the "smartest man in the world" keep them in a computer with not only an obvious password but a prompt that basically says "Password incorrect: you need to ADD ANOTHER WORD"?

Film
  • In You Only Live Twice, SPECTRE not only kept a photograph that they killed a couple for accidentally taking, but they helpfully annotated the back that they killed the couple for taking it, thus providing a clue for James Bond as to where to look.
  • Minority Report subverts and lampshades this. When John Anderton searches Leo Crow's apartment, he finds the bed is covered in photos implying that Crow kidnapped and molested dozens of children (including Anderton's own son). Then it turns out Crow is innocent, and the photos had been faked and set up solely to give Anderton motivation to kill Crow. Later, Detective Witwer examines the apartment, and immediately (correctly) deduces that Crow had been set up, on the logic that real criminals never leave behind this sort of "orgy of evidence".
  • Upstream Color: The Sampler documents all of his victims in some sort of quasi-scientific study, though what he does with this information is not entirely clear. He's never seen studying his documents after the fact and only seems to use his victims to inspire his music.
  • In Hot Tub Time Machine, Adam keeps a box marked "Cincinnati" in his closet, which is apparently evidence of a shameful and shocking Noodle Incident. His friends are horrified that he'd not only keep whatever is inside the box, but plainly mark it "Cincinnati." Adam protests that he can't just throw something like that away, and he had to mark it so he'd know which box it's in.
  • Lampshaded and averted in The Godfather, Michael and Clemenza carries revolver with taped grip and trigger (to prevent fingerprints) and both leaves the gun at the scene to prevent it from being traced back to them.
    "Leave the gun, take the cannoli."
Literature
  • Note to the Reigate Squires in the eponymous Sherlock Holmes story: when the international intrigue hero who's been all over the papers is sacked out in your parlor, that's probably your last chance to destroy anything incriminating. Also, if said incriminating paper has a piece torn off, you might want to wonder about that.
  • In The Fourth Protocol by Frederick Forsyth, a jewel thief plans to burn a briefcase from his latest job (and his fence scolds him for still having it). But it's such a nice one, he can't bear to, so he checks to see there's no identifying marks and keeps it. However it's someone else who gets burned; after his fence is murdered by men searching for the case, he examines it a second time and discovers a hidden compartment full of top secret documents.

Live-Action TV
  • Averted in The Wire; most criminals are always shown dumping their guns into storm drains or, if they can't do that, wiping them with their shirts and throwing them away. Even the otherwise dumb-as-bricks ones are smart enough to listen to their cleverer colleagues and dump their guns. One plot, in fact, revolves around an evidence-dumping gone wrong (one character throws his guns into a harbor, but they land on a barge). The only time a criminal retains his gun is because he has a particular attachment to the weapon, a chromed Makarov, and ends up with life without parole for his sentimentality.
  • In an episode of Hawaii Five-0, once the bad guys steal the evidence that Steve McGarrett's father had been investigating, they keep it for some reason instead of just burning or shredding it, which allows an employee to steal some of it and leak the info back to McGarrett, leading him to the person who ordered his father's death.
  • A heroic subversion in Burn Notice: after Michael Westen is framed for murdering his CIA liaison, the first thing he does is get rid of the murder weapon. By destroying it with thermite.
  • An episode of The Persuaders! involved a crucial piece of evidence that the culprit couldn't work the will to destroy, despite his henchman's urging: A gift by Adolf Hitler himself for helping the defeat and surrender of France.

Video Games
  • Played with Phoenix Wright: Ace Attorney's bonus case, "Rise from the Ashes." The culprit keeps a critical piece of evidence hidden away which he's used to blackmail someone into doing his bidding; revealing this evidence when prompted will have dire consequences, but concealing it (temporarily) will force the culprit to tip his hand, and the new context in which the evidence is ultimately presented points the guilty finger at him instead.
  • Noticeable in Fallout 3 and Fallout: New Vegas. Whenever you get a quest to investigate someone, you usually just need to pick the lock of his vault or hack into his computer to find a note explaining his wrongdoing. It's also not rare to find someone's password written in a fairly conspicuous place.
  • In Dishonored, the Lord Regent has an audio log locked in his personal safe that has him talking about how he not only framed Corvo, but personally released the plague to Kill the Poor. You can then broadcast it throughout the city, leading to the guards arresting him.
    • You can then kill him if you wish as he is being escorted out.
  • In Danganronpa's third case, one character finds an entire hidden room stacked with revelation-packed documents, left there for no apparent reason. The room held enough importance that The Mastermind was willing to come out of their hiding place to attack The Hero via Tap on the Head, who was in the midst of reading a single page before running off with the entire bookshelf's worth.

Western Animation
  • Occasionally happens to some Scooby-Doo villains, who leave out clues all over the place for meddling kids to find.

Real Life
  • Richard Nixon and the Oval Office recordings.
  • A surprising number of Internet criminals (and office workers) either don't know to clear their browser history file and cache, or simply neglect to do so.
    • To a lesser extent, Facebook tends to cause a lot of embarrassing self-incrimination from people who post compromising pictures of themselves where teachers, bosses and significant others can see them.
  • Serial Killers and some rapists tend to keep trophies from their victims. This is sometimes their undoing.
  • The Nazis; after the war, the Allies were astonished at the amount of evidence and paperwork related to the Holocaust they were able to uncover. The sheer amount of incriminating evidence pretty much made the convictions at the Nuremberg Trials a foregone conclusion.
    • Well, they DID start to shred stuff, but only when it was way too late for them. A lot of that shredded material is still being sorted out today.