A gunman who killed nine co-workers at a California rail yard last month was the subject of four investigations into his workplace conduct, and after one verbal altercation a colleague worried that the man could “go postal,” according to internal documents published Thursday. The Santa Clara Valley Transportation Authority, where the May 26 shooting occurred, described the investigations and released more than 200 pages of emails and other documents relating to the gunman Thursday, the Mercury News reported. It was the first time the rail authority has said whether there were w...