California Highway Patrol spokesman Brian Pennings said the shooting aboard a Greyhound was "extremely rare". "In my career I'm not aware of this ever happening," he said, per ABC News.
However there have been high profile knife attacks aboard Greyhound buses previously. In 2008, 22-year-old Canadian man Tim McLean was stabbed, beheaded and partially eaten by 40-year-old Vincent Weiguang Li. Li was later found not criminally responsible and released six years later.
In October of 2001, just weeks after the 9/11 attacks, seven people died aboard a Greyhound bus traveling from Chicago to Orlando, Florida, when Croatian passenger Damir Igrić slashed the drivers throat, before steering the vehicle into oncoming traffic.