Not exactly conclusive proof. Neri could maintain that the “real thief” stole or found his cellphone. I wouldn’t bet money on it, but an attorney could make a case for it as an alternate theory, raising reasonable doubt.
I agree with that. An interview would have to get incriminating statements or there might have been witnesses. It has happened in the that someone dropped a wallet at a scene of a burglary, then when the cops made contact, said that the wallet had been stolen. Without evidence tying the person to the scene other than the wallet, the cops are unlikely to make the arrest.