A gunman opened fire inside a hospital psychiatric unit on Thursday, leaving one hospital employee dead and a second injured before being critically wounded himself. District Attorney Jack Whalen said just what led to the shooting was unknown, but the gunman had psychiatric problems. The victim who was killed was described only as a female employee. A doctor suffered a graze wound and was expected to be released from treatment later in the day. The 213-bed teaching hospital in Darby, just southwest of downtown Philadelphia, is part of the Mercy Health System, a large Catholic health care network serving the region.