Re: The cynic in me says it's academic ...
"It will also look very bad for them if their complaint (however justified) can't be proven - it can be spun as "they were saying damaging lies about the cops" which will not endear them to the jury. "
An example of such police evidence corruption came to light in 1963 with the exposing of the activities of "successful" CID officer Harold Challenor.
It is reported here in his obituary in 2008.