Why should I, as a cop, take someone who robbed the individual in question at face value? I would sooner do an announced search with a warrant. If the guy kills any cops or fights in immediate response to the otherwise peaceful approach only then justify force.
Looking for that big promotion? Salivating over the department's share of loot from seizing his assets?
Exactly. What, the thief is going to tell the 'truth' about the drugs?
Pull the registration data and do a background check on the owner--chances are he's clean, but the thief has priors. This isn't Dr. Watson level, much less Sherlock Holmes.
Only a record of priors by the owner of the vehicle would justify a warrant instead of reporting recovery of the vehicle. The thief had the vehicle, the drugs were in his possession, too, maybe that could be a 'risk' of stealing or receiving stolen vehicles.
If the vehicle owner owned the drugs, too, he'd still be out the stash, even if he wasn't prosecuted, and that can have repercussions that won't be settled in court.