I too thought about it being a hit - but when it was revealed that he returned home and left the $300, wallet, and cellphone in garage I ruled that out since cannot imagine a scenario where he could do that during a hit...
I think if we throw out the dogs not picking up scent at the train station, I'm going with #1 - leaving with or without another and dogs for whatever reason did get his scent. Wonder if car was wiped clean inside?
Still bugs me, why return home at all, simply leave $$, phone, wallet in car - but on second thought shows he was worried car might get broken into and didn't want those items taken..