Trying to Get Rid of Roommate

My question involves a roommate in the State of: Denver, Colorado

Last year in May of 2009 our roommate decided to leave after our lease and left me and my current roommate with an empty room in a really nice house. We wanted to choose the right person but fell short and ended up living with one of our friends who had trouble in the past with his roommate. We thought it was a good idea but discovered it was not. He moved into our new house and within a month managed to get the landlord so pissed at him that the only way he could live there was if he paid a $10,000 security deposit. My friend and I decided that we would rather leave our really nice house insteda of leaving our friend. We both live outside of Colorado and it was up to him to find us a new house. Instread he got high(weed) and found us a cardboard house. Once we move in he instantly tells us he is leaving for the Military in January, which means we left our nice house for no reason. My friend and I found a new roommate and had hin move in but he is not on the lease. We were planning on telling our landlord about him when our "bad roommate moves out" Its now January and everything is horrible. Our "bad roommate" has now become an alcoholic, dropped out of school, pops massive amounts of pain pills (Vicanin), steals our food and alcohol, and constantly cheats on his grilfriend of 3 years and tells us not to say a word even though his grilfriend is ablsouty in love with him and is a nice girl, and has absolutly no money even though he works 5 days a week.He always treats our friends horribly and last week he tackled a girl for no reason and left her face bloddy and thought it was ok and funny. He has crashed into my car twice from driving home drunk and both times drove away and played it off as if he didnt do it but I saw him both times. We all hate the kid and our new roommate absoulutly hates him but broke his other lease to live in our house with the thought that he was going to leave. Are there any legal actions we can take against him, such as saftey for us becasue he is mentally unstable?

Did you have the bad judgment to put your names on the lease along with his? If so, you'll need to try to work something out with your landlord.