If a vehicle was stolen and there was weed in it how would the police know if it was the suspects

if a vehicle was stolen, and the police found it..and it had marijuana in it, how would the police find out if it was the suspect who stole the vehicle or the owner who owns the vehicle

In most states the operator of the vehicle is supposed to know what's in it the same as he/she should know who owns it. There are many ways the police could "find out," depending on the evidence. Was the driver in the vehicle when arrested? Was there any evidence he/she was using the drugs? If there is other property in the bag with it, who owns that? Was it in an area like the glove box or hidden under the spare tire? A person that steals a car would surely look in the glove box to see if there is anything else of value there. The police would weigh all of the facts and make that decision based on the evidence.