This would probably not be grounds for a lawsuit.  Lawsuits for defamation require that the published statements be false and damaging to a person's reputation.  (A Fisherman's Best, Inc. v. Recreational Fishing Alliance, 310 F.3d 183)  In your situation, the university police found drugs.  The university police's statements that the roommate was in possession of contraband were true.  You cannot sue someone for defamation if the statement was true, even if the statement damages your reputation.  As to the alleged improper search and seizure, because this happened in a college with college police, the regular rules governing police may not apply. However, police are generally permitted to ask people to let them look in locked areas. If the police do not have a warrant, the roommate could have refused to allow the police into the locked areas. But, because the roommate let the police in, they probably have no grounds for an improper search.