I recently gave someone (Bob) a ride in my vehicle to a local supermarket. I remained in the vehicle, and Bob went inside. Bob stole something from the supermarket, and loss prevention attempted to detain him in the store. Bob ran away and got back into my car, without telling me what happened, so we left. A witness saw what transpired, and gave the store my cars license plate info and description. My question is this: Since I never left the car, went inside, or knew what happened, can I be held criminally liable for Bobs theft?
No. To be charged for "aiding and abetting" or as an "accessory" to the theft, you need to have both:
known about the crime and
acted to help carry the crime.
Someone who unknowingly helps carry out a crime cannot be charged with aiding or abetting.
Obviously, since you didn't know beforehand that your friend was going to steal from the store, you can't be charged for that. Whether you can be charged with "aiding or abetting" after-the-fact depends on when you found out, and what you did with that knowledge. Suppose you lied to the police to give Bob an alibi, or helped him sell the loot. Since in those instances you knowingly helped him carry out his crime, you could be charged.
Have you satisfied the legal elements for a crime?
Laws against stealing generally have a high mens rea requirement, so given that you had no intent to facilitate a theft, you are probably not guilty, but one would have to look at the exact statute to be sure.
Can you be held criminally liable?
As a practical matter, this is a separate question. A judge would likely find that the facts in this case support probable cause that you participated in the theft. So it is possible for you to face criminal charges. You would then have to convince the triar of fact that the claims you have made regarding your lack of knowledge are true (or, at least, it is reasonable to doubt that they are false).