It is the state's job to prove you guilty. Is there any video evidence of him walking out of the store with the merchandise? Will he take responsibility and tell the authorities that you had nothing to do with it? In criminal law, the state is alleging that you are an accesory to your cousin's taking of the goods. You are free to testify that you had nothing to do with it. How long have yo worked for the company? Have you had any other issues? Do you have a clean record? The state has to show some nexus between you and your cousin's theft. They do not have to prove your guilt beyond all doubt, but simply beyond a reasonable doubt. Good Luck
I agree that the prosecutor will have to prove a connection between your cousin's criminal conduct and you. The surveillance tapes (if any) maybe very helpful in your defense or it could be used as circumstantial evidence of your guilt. It will depend on how suspicious your behavior appears on tape. My guess is that your cousin said something to incriminate you and/or he said something inconsistent with what you might have said to the police. Keep in mind, though, whatever the cops put in their report regarding statements from suspects is always a biased after-the-fact summary that may be distorted or inaccurate. In any event, the police report should contain facts, opinions, speculation re the supposed connection.
A skilled defense attorney will be able to point out where the prosecution has failed to prove its case.