Dear Health,
Why would the thief be a rodef as soon as he breaks in? Maybe the house is empty. [As well as a hundred other variables.]
How do you know he was about to drive the car? Maybe he was going to sleep it off. (Among other possibilities.)
I propose the cop should have confirmed that he was the guy who bought the cigarettes. [Maybe he did.] Then ask him where he got the money from. [I am not sure how the best way to ask this question. But something along these lines. Then again, it could be the cop did this too.] The he could have asked him if he needs a ride. [Maybe he did. Maybe something happened here. It is not clear to me.] And then he could have left him alone! [Only one of the millions of Americans that were intoxicated at that moment.]