Having been the foreman on two juries where it quickly became evident the the police were either lying about what they saw the defendant do, or completely incompetent, I'm afraid I would need a little additional proof.
If that's your standard -- no one would ever get convicted. Because the forensic "expert" (an employee of the police department) testifying as to if the fingerprints match or not could also be lying or completely incompetent. At some point you have to take the tin-foil hat off.