In the UK, a prosecution would fall apart if police officers were cross examined and had to admit that they were hiding evidence. The procedures for handling e

In the UK, a prosecution would fall apart if police officers were cross examined and had to admit that they were hiding evidence. The procedures for handling evidence are very strict, and police are obliged to register everything in a database (I don't know the name of the laws forcing them to do this, but it was explained to me when I was on a jury). You then have both the officers who were on the scene and the master of records, where video evidence is used, testify about the source of the video and any processing it has been through, and so on. These prosecution witnesses are all cross-examined, and if a defense lawyer had the angle that procedure had not been followed properly (i.e. the master of records, and those investigating the case, had ignored or hidden evidence that supported the defense), the officers' testimony would fall apart and they would likely be charged themselves (or at least disciplined internally) on the basis of the evidence they gave in court under oath.