Legal Question in Civil Litigation in Maryland

You can sue him based on negligence. Of course, you should try to negotiate with him before you sue. Did you file a police report? Did he admit he left the door open?

You said he left the door unlocked. However, without evidence of his negligence, you may have a hard time proving he is liable.

Even assuming that your roommate was negligent, the thief was acting intentionally. Where one person's negligence enables another person to commit an intentional tort, the law will ordinarily hold only the second person liable. There may be reasons why your case should be treated differently. That will depend upon details you haven't provided.