LOL, nobody knows how to steal a vehicle! There is a little appliance you can buy which you have to put in the keyhole, it makes a replica, very quickly, so when you "test drive it", you make a replica and then come back later to steal it. Perhaps whomever was driving was trying to do that but Bosma saw him, in a panic to avoid being caught for theft, one of them killed Bosma. Didn't they also steal other vehicles that Dellen could have afforded to buy, but chose not to, but they didn't kill anyone?
From the Babcock trial and I always wondered why Dellen would hang around Smich, it seemed as if Smich was either black mailing Dellen because he kept asking Dellen for money or a "mission" and Dellen would send an "irritated reply" but also pay whatever debt Smich had. Police seem to think he was keeping Smich around for his help/loyalty in the Babcock murder, which was his first murder and then after that, the two had to stick together since they had burned the body together. Is it possible that he didn't have any friends, was not in an academic environment where it's acceptable to not have a very active social life, but in business, where "networking" is key, so he picked up whatever friends he could and just seemed to attract the Smich type and not the type that would be of value to his legitimate career/business? Was Smich blackmailing him for something previous to the Babcock murder such as theft, drug dealing? Is that why Dellen kept paying Smich who would send him texts while he was on a airlplane materials course in the U.S to ask for money? Saying he either needs money or a mission and then sarcastically saying "or I could get a job and be the person everyone wants me to be".