Busted, he didn't put up a fight, company officials said.
"He was calm. There were no signs of anger, or threats of violence," said Gregg Adler, a lawyer for the Teamsters Local 1035
He quietly signed a letter of resignation and was headed for the door when he pulled out a gun and started firing
A source tells CBS News that just before 7:30 a.m., Thornton used a handgun to shoot the two men who fired him. He then went to the warehouse. As employees were loading beer onto trucks Thornton allegedly ran along the loading platform selectively shooting - killing some and sparing others.
In the end, Thornton killed eight people, injured two, then turned the gun on himself in a that union and company officials said they would not have anticipated from someone with no history of complaints or disciplinary problems.
Yet relatives say Thornton, 34, finally cracked after suffering racial harassment in a company where he said he was singled out for being black in a predominantly white work force.
"Everybody's got a breaking point," said Joanne Hannah, the mother of Thornton's longtime girlfriend.
After shooting his co-workers, Thornton hid as police moved in. He called his mother, who tried for 10 minutes to talk him out of killing himself, his uncle Will Holliday told reporters.
"He said, 'I killed the five racists that was there that was bothering me,"' Holliday said. "He said, 'The cops are going to come in so I am going to take care of myself."'
Authorities said they found him dead.
9 Killed in Conn. Workplace Massacre
Thornton had said he found a picture of a noose and a racial epithet written on a bathroom wall, said Hannah, of Enfield, whose daughter Kristi had dated Thornton for the past eight years. Her daughter told her that Thornton's supervisors said they would talk to his co-workers.
Brett Hollander, whose family owns the distributor, denied any racial bias. And a union official said Thornton had not filed a complaint of racism with the union or any government agency.
"I can assure you there has never been any racial discrimination at our company," Hollander said.
Teamsters official Christopher Roos said, "This is a disgruntled employee who shot a bunch of people."
Company vice president Steve Hollander told The Associated Press he was stunned by Thornton's rampage after a meeting in which he calmly agreed to resign instead of being fired:
"He was cool and calm. He didn't yell. He was cold as ice. He didn't protest when we were meeting with him to show him the video of him stealing. He didn't contest it. He didn't complain. He didn't argue. He didn't admit or deny anything. He just agreed to resign. And then he just unexplainably pulled out his gun and started blasting."
Steve Hollander said he thinks Thornton had guns stashed in his lunch box. The executive said two people standing near him were fatally shot in the head, but he was only grazed in the jaw and the arm.
"He shot at me twice and hit me a couple times," he said. "By just the grace of God, I don't know how he missed (killing) me."
About 50 to 70 people were in the Hartford Distributors warehouse about 10 miles east of Hartford during a shift change when the gunman opened fire, said Brett Hollander, Steve Hollander's cousin.
The shooting was over in minutes. The victims were found all over the complex, and authorities said they didn't know whether Thornton fired randomly or targeted people.
Workers flooded out of the building as police officers raced into it, Manchester police Chief Marc Montminy told the town's board of directors Tuesday evening.
"Some were hiding in the woods and some were hiding under cars," he said.
State police found weapons in the suspect's car, Montminy said, without providing details.
Thornton was not a problem employee and had not had any previous disciplinary issues, Adler said. He said he was not aware of how much beer Thornton was accused of stealing.
Kristi Hannah had been with him Monday night and had no indication he was planning anything violent, her mother said.
Joanne Hannah described Thornton as an easygoing guy who liked to play sports and video games. She said he had a pistol permit and planned to teach her daughter how to use a gun.
Police declined to release the names of those killed.
It was the deadliest U.S. shooting since 13 people were fatally shot at Fort Hood, Texas, last November. A military psychiatrist is charged with 13 counts of premeditated murder and 32 counts of attempted premeditated murder in that case.