That depends on what you mean by blame. If I were say the father of a child that left the car unlocked and the car got stolen. If we managed to get the car back, there's no way in hell I'd let that child use the vehicle anymore, and I'd sure as hell be pissed at them. I don't think they're morally at fault or anything, they just acted stupid and now the household has one less car. The same could be said if they were renting a car and left it unlocked. Yes, the thief is the one morally in the wrong, but the person entrusted with the car is the one making intellectually poor decisions. Someone can be a morally upstanding citizen and still be considered incompetent, just like a smart individual could be seen as a morally bankrupt evil bastard, the difference of it all hinges on what sort of blame you're allocating. The scenario with the child, they would suffer the consequences of their actions by no longer being allowed to use a car that they have not paid for. If they want to use a car, they have to pay for their own, so if they make poor decisions again, that's on their head, not mine. If I'm just a cop filling out the report, I'll go after the thief, but I may still tell the individual to lock the car next time, not reprimanding them or anything, just explaining that there was something they could have done that would help prevent this scenario happening again.