Legal Question in Criminal Law in California

Sure. Charges are based on what the prosecutors believe. They don't have to believe what suspects and witnesses say, even when they say it under oath. Neither do judges or jurors.

If the defendant really didn't know the drugs were on his person then he's not guilty of possession. But a very large percentage of defendants make that claim, and it's rarely true -- even when another witness will back it up.

A prosecutor is rarely going to take the claim seriously and believe it. Anyone dumb enough to do that for you risks you both being charged with 'conspiracy'. Not a good 'deal' for either of you.