Thornton had signed a one-line resignation letter after he was confronted with video surveillance evidence that showed him stealing alcohol from the distributor. A moment later, Thornton requested a drink of water and went to a nearby kitchenette where Davis said he had stowed his weapon-packed lunchbox.
Thornton used two 9mm handguns during the attack, and authorities later found another shotgun and extra clip of ammunition in his car. Davis said that it is believed the three guns were purchased at an East Windsor gun store. Hoffman's Gun Center, a store in East Windsor, is listed on Thornton's Facebook page.
Wilbert Holliday, Thornton's uncle, told ABC News that he didn't think the shooting was random and that his nephew had complained about racial discrimination at work.
Holliday said that Thornton called his mother after the shooting spree and talked to her for about ten minutes, telling her, "I killed the racists that were bothering me."
According to Holliday, Thornton had filed complaints with the Teamsters union about alleged racial harassment and had pictures on his cell phone of the N-word and a hangman's noose scrawled on a bathroom wall at Hartford Distributors.
Union representatives strongly denied the allegations.
Gregg Adler, a union attorney, said Thornton had never filed a harassment complaint with the union, but had filed a separate grievance that had been settled in his favor regarding insufficient training. Adler said that it was clear Thornton knew the protocol for filing a complaint.
Asked about the union's denials that Thornton had filed a complaint, Holliday said, "Of course they're going to say that."
The newest employee of the distributorship's 65 drivers, Thornton began shooting at what would have been one of the busiest times of day at the warehouse.
"It couldn't have been a worse time of day," said John Hollis of the Teamsters Union. "The day shift was coming in and the office staff was all there. It was the time of day where the most employees would be in the building."
Davis said authorities believe about 50 people were in the building at the time of the shooting.
Early Wednesday Manchester police released the names of those who died in the shooting. Among the dead are 57-year-old Francis Fazio Jr., 56-year-old Douglas Scruton, 49-year-old Edwin Kennison, 51-year-old William Ackerman, 51-year-old Bryan Cirigliano, 60-year-old Craig Pepin, 50-year-old Louis Felder Jr. and 61-year-old Victor James.
Police listed two men survived gunshot wounds. In addition to Steven Hollander, 77-year-old Jerome Rosenstein is in critical condition at Hartford Hospital.
ABC News' Clarissa Ward and Bradley Blackburn contributed to this report.