It's been said, "Once a cheater always a cheater." Does the same apply to a thief?

There is a guy who quickly moved in with one of my friends after barely even knowing her for a few weeks. She's happy because he spends money on her and helps her to pay the bills.(He does work, earning money legally, respectfully) Prior to now he was in prison for 10 yrs. for robbery. He does seems really nice, even though he has a past of stealing. One of my friends doesn't trust him, says he's just a loser and I shouldn't trust him around me, because a thief is a thief, period. What are your opinions? I believe some people can change but I do find I am locking things up more than I ever used to, just in case!