Police officers do not have the right to destroy or change evidence. Even if the evidence makes them look bad officers cannot take that right into their own hands If all of the laws are followed they don't need to worry. If laws are broken even by accident officers should have to face the punishment just like everyone else.
Police are not judge or jury. They have no judicial authority. Their responsibility is to arrest and question suspects, not determine guilt or innocence. At some point, it no longer makes sense to continue storing evidence for presumably solved cases. If a generation has passed and there is no one to challenge a ruling in a case, then by all means the evidence needs to be destroyed in order to make room for evidence in newer cases. Until then, it needs to be stored so that it can be further evaluated if necessary.
Police officers are citizens and therefore need to follow laws just like us, Americans. If it would be unlawful for an American citizen to destroy evidence (Ex. throwing away marijuana on a possession charge) then it would not and should not be okay for police officers to destroy evidence to further their cause. It would only lead to a further abuse of power and more shootings because then they could destroy the evidence of a bad shooting and lead to further racial divide (since most of these shootings are of black citizens).
Police should not be allowed to destroy evidence. I can't imagine a situation where this is a good idea. Wouldn't this contribute to the wrong people being found guilty or innocent? This sounds like a concept out of a bad TV show. Police should never be allowed to destroy evidence for any reason.