A serial rapist spotted on surveillance video appears to be stalking alumnae of a particular sorority in Dallas, police have revealed. Four members of Delta Sigma Theta have been raped in their homes in the last 11 months by an attacker who had personal information about them, reports the Dallas Morning News. The women were all in their 50s or 60s. The sorority has sent out email alerts to alumnae, and police have requested rosters of past and current members. (More rape stories.)