Destroy the Evidence

Here's how to dispose most incriminating evidence. By burning.

Our hero, or another good character, has come into possession of some evidence relating to a crime. However, instead of turning this evidence over to the proper authorities, the hero destroys (or withholds/hides) the evidence.

Why? Well, there's a number of reasons. For instance:

The evidence could incriminate someone else who the hero likes and doesn't want to see punished.
The evidence, if made public, will ruin the victim's life (or the life of someone involved in the crime).
The hero is being blackmailed by the Big Bad or an associate.
The hero would be incriminated by the evidence.
The evidence contains information which would exonerate another villain who is on trial for another crime.
The evidence, if involving a dead person, might cast a bad light on their memory—and the hero was a good friend/relative/lover of the dead person.
The evidence is entirely worthless—it's too late to act.
The hero wants to punish the bad guy himself.
While the evidence could get the bad guy put away or otherwise punished, it would cause scandals and create chaos for a lot of people, some who may be entirely innocent.
The evidence would reveal an ugly truth about a past event that the public perceives as a good thing, and the hero wants the event to stay a good thing.
The criminal committed the crime for a good reason, and in retrospect the hero agrees that the act was justified.
The crime involved the murder of someone who was a truly terrible person, and the hero doesn't want the evidence revealed, since it would result in someone going to prison for something he doesn't think of as a crime.
The hero is currently on the run or at least not on good terms with the local authorities, so he can't give the evidence to them without being captured/killed/arrested.
The hero is actually the villain.
The hero believes that the criminal is genuinely repentant and need not be punished further.

Whatever good intentions the hero may have had, destroying the evidence will probably have bad results — a villain could walk free (or somebody could Give the Villain a Hero's Funeral), for instance. May result in a What the Hell, Hero?.

As an Ending Trope, Spoilers ahead may be unmarked. Beware.

Examples of Destroy the Evidence include:

Comic Books

The Sin City story "The Big Fat Kill" involves destroying a decapitated head in order to avoid a Mob War between the Mafia and cops with the local prostitutes caught in the middle.

Literature

There's an accidental case in Dead Man's Chest by Kerry Greenwood. At a wake held for a dead woman, Phryne steals a pillowcase dropped by a maid that she finds to be suspicious- it has teeth imprints and a stiff patch, indicating that the old woman was murdered by being smothered with the pillow. At the end of the novel, Phryne's maid Dot washes the pillowcase and returns it, not realising that it was important.
In one of the Lord Peter Wimsey stories, he discovers the identity of the murderer, who was a Sympathetic Murderer, and tells his friend, a policeman, a hypothetical story of who he thinks is the murderer and how it happened (he's actually telling him the real story) but since another has confessed and later killed himself, the policeman tells him to let it drop. Wimsey later reflects that he could, if he wanted, prove the case, though he doesn't want to.
In Players of Gor Cabot learns of a plot by Cos, Tyros, Brundisium and certain factions in Ar to attack Ar. He gets the evidence, then learns that it's actually happening right now. The evidence is now worthless so he burns it. Plus he plans to exact his own revenge.
The Horatio Hornblower short story "Hornblower and the Widow McCool". The British occupying forces and Irish rebels have recently achieved a fragile peace in Ireland. Hornblower discovers letters to rebels not known to the authorities. If he turns the letters over to the authorities, they'll go after the rebels and cause another outbreak of violence. He decides to throw the letters overboard instead.
In the Discworld novel Men at Arms, Captain Carrot destroys the evidence that he's the rightful king of Ankh-Morpork, because he doesn't think it needs a king anymore.

Live-Action TV

In Veronica Mars, Logan comes into possession of the sex tapes of his girlfriend and his father, and he destroys them so they wouldn't be seen in court and ruin Lilly's memory.
In one episode of NCIS, Gibbs switches tissue samples so that it will appear that a body they're trying to identify was that of a dead Marine- the Marine (who is dead) had had a kidney transplant from a friend, who was still alive. Because you can't be a Marine if at some point in your life you donated an organ, the Marine, if this became known, would have to quit- which he really didn't want to do.
- Another NCIS example. In the end of one episode Gibbs realizes that a bad guy was killed with the prayer beads of a man the bad guy himself murdered, a marine and the son of a local Imam. Gibbs knows that this means the marine's father killed the bad guy to avenge his son's death, and the Imam should be arrested for murder himself. But when Ziva mentions that the prayer beads belong to the original victim Gibbs denies it, and she let's it pass.
In a season of The Dukes of Hazzard the phrase "The boys got off, because there wasn't any evidence" is about guaranteed to occur in at least a third of the episodes. Frequently the lack of evidence is a result of it being sunk in a pond, set on fire, blown up or in some other fashion destroyed. Sometimes the destruction is even intentional.
- Riffing on the Dukes of Hazzard one, one time they were being chased for having made moonshine but got off because they used it as fuel for the General Lee and had run out of "gas." (Which I guess would be another Eat the Evidence example, for a given definition of "eat.")
At the end of at least one episode of Jonathan Creek, (" The Scented Room" is the one I'm thinking of, although it may also have happened in " Devil's Chimney") the title character lets the culprit go, on the grounds that they're not really that bad.
Dexter has been known to mess with or destroy evidence to en*sure that particularly bad criminals go free... so he can hunt them down and kill them instead of letting them have a government-sponsored vacation at prison.
In the season one finale of In Plain Sight, Mary hides cocaine from the police and Marshall Service to protect her little sister. The final shot of the episode is of the back of a line-painting machine on a football field, implying that this is how she got rid of the evidence.
CSI: NY The Fall. Don Flack's mentor, Moran, finds out that his son was involved in the robbery of a bodega. He subsequently disposes of the incriminating pop can he finds to keep the boy out of jail. This results in Broken Pedestal and Mac and Flack having to arrest him.
Dragnet had it once or twice. One episode involved a bookmaker destroying his paper trail, which was written on flash paper, a quick burning type of paper. Friday luckily stopped him before it all went up in flames.

Music

Unusual Music example: Billy Talent song "Burn the Evidence."

Newspaper Comics

There's a Far Side cartoon with a rat in a prison cell telling his cellmate, "I would have gotten away scott-free if I'd gotten rid of the evidence... But shoot, I'm a packrat."

Theatre

Love's Labour's Lost: The King and three lords in his attendance take an oath not to woo any women for 3 years; then some women show up. The King and two of his lords are caught writing love notes by the fourth who berates them; then the love note that he wrote is brought forth by some rustics, so he tears it up before anyone else can read it. (In a production I was recently involved with he even tried to Eat the Evidence.)

Video Games

Heavy Rain: Scott Shelby burns the evidence he finds relating to the Origami Killer...because he is the Origami Killer.
Persona 4: Adachi, who is both the murderer and a detective working on the case, admits to destroying certain bits of evidence.
Done multiple times in the Ace Attorney series, usually by the defendants. Often they're trying to protect someone they care about from incrimination, even at the cost of their own freedom:
- In case 1-5, Lana Skye deliberately distorted evidence relating to the SL-9 incident partially in order to get Joe Darke convicted, but mainly to prevent her sister from being charged with murder. Later, Phoenix doesn't want to present a certain piece of evidence for the same reason - it implicates someone he doesn't want to see get in trouble.
- Phoenix Wright himself does this in 3-1 by eating Dahlia's locket.
- Special mention to Detective Badd in Ace Attorney Investigations who destroyed evidence relating to the Yatagarasu. As head of the investigation he was in a perfect position no traces were ever found at the crime scene. Why? He was a member of the Yatagarasu.

Web Original

In the Whateley Universe, Kodiak destroys tapes of the Don (and probably more of the Alphas) abusing and raping Skybolt and Cavalier, who were Mind Raped into being obedient slaves because he knows that should the tapes get out, sooner or later the entire school would see them- and any chance of Skybolt and Cavalier having a normal life once they get released from the psych ward would be ruined.

Western Animation

Invader Zim: Zim does this in a bathroom screaming "LEAVE NO EVIDENCE!"