"Today I met with Shawn. We had a good meeting and I informed him that we wouldn't be re-signing him," Chiarelli said in a video posted on the team's web site. "It was good in the sense that we talked about the time Shawn has spent here. ... I told him that he was one of the most significant acquisitions we made, one, for the role that he played, and two, for the person that he is.
"It was nice to rehash his time. It was sad to tell him that he wasn't coming back. I wished him well and Shawn was real up front about it. I wished him luck and I'm sure he'll have success with his next team."
Thornton, 36, signed with the Bruins after winning a Stanley Cup with the Anaheim Ducks in 2007. He's been a fourth-liner and the Bruins' enforcer ever since, helping them to a Cup victory in 2011.
"It was seven amazing years," Thornton said. "I've been asked for my favorite memory and I don't know because the whole thing has been an amazing experience. To do my job in this city for seven years has been incredible. Unfortunately, it's time to move on but it's part of the business. The Bruins have been nothing but first class treating me unbelievable and I'm very thankful for the opportunity."
Thornton said that while he would have liked to stay in Boston, he wasn't shocked by the move.
"People had asked me for the last month and I said I thought it would be a coin flip," Thornton said. "So surprised? No. Either way, mentally, I knew a decision was coming.
"We'll see what the interest is and hopefully there's a lot," he said. "It's tough to leave but I'm excited for what comes next."
This past season was a turbulent one for Thornton, who was suspended 15 games for sucker-punching Brooks Orpik and endured criticism and was fined $2,820 for spraying Montreal's P.K. Subban with a water bottle in the final minute of a playoff game.
Chiarelli appreciated the physical presence Thornton brought to the Bruins.
"He was able to form one third of maybe the best fourth line in hockey for the longest time," Chiarelli said. "And of course there's the pugilistic component of his game, which is an important part. He was very good about that. It was a job that not a lot of people like to do but it's a job that's important."
ESPNBoston.com Bruins reporter Joe McDonald contributed information to this report.