Re: causitive-passsive meaning...
We don't leave a key in the ignition switch. We just leave the key in the ignition. "Forgot" doesn't work here either.
If you want to say all of that, you don't need two sentences:
Jim had his car stolen last night because he left the key in the ignition.
Jim had his car stolen last night because he forgot to take the key out of the ignition.
Jim's car was stolen last night - he had left the key in the ignition. Idiot!
You can't assume that he left the key in the ignition just because he had his car stolen though. The thieves may have simply smashed a window and hotwired the car.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.