Authorities have investigated at least 86 cases of sexual violence against elderly and disabled residents of Chicago nursing homes since July 2007, but only one of those cases resulted in an arrest, a Tribune investigation has found. For their part, police sometimes drop their investigations too quickly when faced with the host of obstacles from both victims and facility employees, said Ronald Costen, a former criminal prosecutor who directs the Institute on Protective Services at Temple University’s Harrisburg Campus. "You have to treat these cases of sexual assault in a long-term care setting like coming across a dead body on the side of the road — you have to look for hard, forensic evidence," Costen said.