A warrant is not always needed, depending on the totality of the situation.  Exigent circumstances, where evidence is likely to disappear, is one major exception. But again-it depends on the entire situation, which is often vague and fluid. But I would think the deck is stacked in favor of "exigent circumstances" being present for a vehicle that contains, or recently contained, a gunshot victim. Proper procedure in that case would be to do a cursory search and if anything is found then the vehicle is held and a warrant is applied for,