He does not need evidence which proves that he is not guilty. He needed evidence which made it less likely that he committed the crime. Burden of proof is always on the prosecutor. The fact that the receipt timestamp does not make him 100% "innocent" is irrelevant to whether it makes it less likely that he is guilty.

If he did not pursue enforcement of his subpoena back at the time Hertz did not comply, his case is going to end rather quickly now.