UPDATE--
Talked to the cops, they have no idea what could have happened in the bathroom. I give up. I will ask the "ring leader" of the party, but don't know if I'll get an answer.
I found out how the kids got in...my difficult child left a window open. Probably the one in his room. It's basement level and I didn't go in his room before we left to check things out. The air conditioning was on and I just naturally figured no one would've opened a window. Stupid me! Unfortunately, $300 cash was stolen. $200 of my daughter's babysitting money that was in her dresser drawer and $100 that I had in a drawer that was next to my bed (that I had set aside to send to a local family in need of financial help because of the father's terminal illness). Extremely upsetting. I've reported it to the police and they will investigate. But I have little hope of getting it back.
The good news is all the keys are accounted for and no one that shouldn't have a key has one. Including my son. He never did, so couldn't have made a copy.
I haven't kicked him out yet. It's the next step. One more issue and he'll have to leave. I've told him so. Please don't beat me up for that. This whole situation is new to me and I'm taking it one step at a time. My son can't drive our cars and I've turned off his cell phone that I pay for. He's feeling the hurt. I've challenged him to stop smoking pot for a week. He says he can do it. I told him that I'll ask him at the end of 7 days if he was able to do it. Only he will know the truth, because of course I can't trust him. He'll know in his heart if he's successful. Also, I found a LADC who is a former addict that I'm going to send him to.
THANKS SO MUCH for ALL the help and ideas that were thrown around. I do know that no one has smoked pot in my bathroom. If you knew the layout of our house, you'd understand...it wouldn't make any sense to risk doing that.