Fantastic movie! Question about the ending...

I think it was because he saw himself in baby when Deborah showed up as he stated he loved once, so i'm guessing he lost her due to his work and he didn't want the same for baby and to be honest it wouldn't have cost him much to help them just a bit of money which he had plenty of. Also he didn't know gunman would be waiting for him in the car park

As I saw it he was a hard man in a hard profession with his own moral standards but who still felt a bit of guilt and responsibility for dragging Baby in to the job. Actually that very noirish now that I think about it. When everything fell to pieces he does the right thing as he sees it and try to help Baby and Debora - which probably didn't work out as well as he'd expected.