[aristeides]

In that case (of the sniper telling the police that the witness was lying,) the police should believe the (perhaps merely alleged) sniper and not the witness, exactly why?

[ARCADIA]

should believe the (perhaps merely alleged) sniper and not the witness, exactly why?

They would know it's the sniper because, if in writing, the dogs would pick up the scent on the paper. Then the information would be taken in context and be determined to be more credible than the witness.