A representative of Hartford Hospital, where three of the shooting victims were treated, confirmed to ABC News that one of the victims had died, while the two others were in critical and fair condition but were expected to survive.
The victim who died at the hospital has been identified as 59-year-old Victor James.
James' mother, Gloria Wilson, told the Hartford Courant that her son had been looking forward to retirement, when he would be able to spend more time with his two daughters and four grandchildren.
"There wasn't a better family man," Wilson said.
Another victim killed in the shooting was Craig Pepin, 60, according to friends.
A driver at Hartford Distributors who had three sons and a daughter, Pepin was a soccer coach for a travel team with the South Windsor Soccer Club. He recently played on a softball team with the South Windsor recreation department. His team won its game Monday night, friends said.
Hartford Distributors is one of the state's largest beer distribution companies, headquartered in the town of Manchester, Conn.
Authorities rushed to Hartford Distributors just after 7:30 a.m., after someone called 911 saying, "Someone has been shot and there is a victim down," Manchester Police Lt. Joe San Antonio told reporters.
"He was the newest guy of about 65 drivers," Hollis said of Thornton.
According to Hollis, Thornton opened fire at what would have been one of the busiest times of the day at the distributorship.
"It couldn't have been a worse time of day," said Hollis. "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."
Hollis estimated that 65 employees would have been at the scene at the time of the shooting.
Thornton was listed as living in East Hartford, Conn.
Connecticut Gov. M. Jodi Rell called the shooting "a senseless act of violence that has left us all shaken and reminds us just how precious and fragile life truly is."
"In the coming days, we will learn more about what happened. We will likely never fully understand why it happened," said Rell in a prepared statement. "But an inexplicable -- and indescribable -- catastrophe such as this is a cruelly clear reminder that we must take time in our daily lives to appreciate how what we have."
WABC-TV and WTNH-TV contributed reporting to this story.