I believe they have to prove beyond a doubt that u stole it. There word against yours, right?
They have to present evidence to support their contention and so do you,,then after both sides have presented the facts a jury determines who has proven or failed to prove guilt or innocence based upon the evidence presented by each side.
Simply saying you didn't do it when they took the item from your possession is a loser.
If you have no witnesses and no documentation to support what you say and counter the evidence of the prosecutor..all he has to show is the item was stolen and you had it.....you lose.