I've had experiance with this...
Initially, you'd want to ask him about it, but don't know exactly what to say, when to say it, and how to say it.
You say he's been a little more than unruly, so you have reason to believe that if you ask him about his "walks" and him always having money when he has no known legal legitimate job, that he will be a little more than "defensive". And that's fine...But, if he is downright angry about you asking him about something like that, then something is wrong.
Personally, I would put him out of the house because if your intuition is right, he is a danger to your house and home. But you don't want to do that because it seems to me that you are a caring mother, and you have that attatchment.
If you are right, please don't think you have done something wrong as a parent. Because it is not true. A person is who they are because of the people they surround themselves with. And negative people like that have large impacts on the life of a young man.
So...all I can say is get some help...And if he doesn't want help, then I don't know what to say because you can't help someone who doesn't want to be helped.
I hope I helped you..