Illinois: When Gary Martin came to work at the Henry Pratt valve manufacturing plant in Aurora, Illinois, on Friday, he was told he was being terminated from his job.
Shortly thereafter, Martin pulled out his Smith & Wesson revolver and opened fire.
Aurora Police Chief Kristen Ziman said Martin shot six fellow employees, five of them fatally, at the sprawling warehouse where he had worked for 15 years, and wounded five police officers before he was slain by police 90 minutes later.
She said police had yet to determine whether the shooting was an impulsive act or premeditated, and that investigators had not immediately ascertained why he had been fired.
She said police were executed a search warrant at his residence to further their investigation of what she called a "workplace shooting". Jeremy Sherman, a neighbour of Martin's at Acorn Woods Condominium Complex in Aurora, about 64km west of Chicago, told Newsweek's Daily Beast website that Martin could often be found outside playing with his remote-control toy cars and drones.
Sherman described his neighbor as a loner with whom he sometimes chatted without ever learning anything about Martin's work life or his past. Sherman said he never saw Martin with weapons - or with guests.
"He kept to himself a lot, and he was always on his porch," he told the Daily Beast. "Even when he wasn't doing nothing, he'd be out there sitting. I'd be out there, sometimes one, two [o'clock] in the morning and he'd be there just sitting all in the dark, [in the] shadows."
Martin's mother told the Chicago Sun-Times that her son had been "way too stressed out" recently.
Public records showed Martin had a criminal past, a 1995 conviction for aggravated assault in Marshall County, Mississippi.
Aurora Police Chief Ziman said authorities did not know if he had legally purchased the gun he used. Convicted felons are barred from buying firearms.
A fellow employee and eyewitness John Probst told CNN that Martin fired his pistol with a green laser sight at fellow workers. "What I saw was the guy running down the aisle with a pistol with a laser on it," he said.
The shooting came a day after the one-year anniversary of the massacre of 17 people by a gunman at Marjory Stoneman Douglas High School in Parkland, Florida.