Petey is the name of a former restaurant employee who came back to shoot his former boss at the restaurant and later at Seattle Grace Hospital.
Petey was fired from his job at a Seattle restaurant. Shortly after this, he returned to his place of work armed with a gun and began to shoot. He injured 14 and killed 2 before fleeing. He escaped and was at large until he came to the hospital where his victims had been taken. When he saw Brad Ackles, his intended victim, outside the hospital, he shot him as well as Preston Burke before shooting himself in the head in an attempted suicide.
He wasn't killed instantly and was taken into the ER to be treated. When Cristina heard that he had shot Burke, she tried to resuscitate him despite the odds, not wanting him to get out of it by dying.
He was married, but told Joe he wasn't a good husband. ("Overheard at the Emerald City Bar")
He told Joe he wasn't a good father, indicating he has at least one child. ("Overheard at the Emerald City Bar")
Petey worked at a restaurant until Brad Ackles fired him.