Police said they are acting on a request by Quebec's director of criminal and penal prosecutions, Louis Dionne. After evidence is collected, it will be determined if there are grounds for prosecution, they said.
But Pacioretty said he doesn't want Chara prosecuted.
"I sincerely appreciate all of the support that I have received since my injury," he said in a statement. "I was disappointed that the NHL did not suspend Zdeno Chara. However, I have no desire for him to be prosecuted legally. I feel that the incident, as ugly as it was, was part of a hockey game.
"I understand that this is not my decision. I have respect and admiration for the authorities in Quebec. I simply wanted to make my opinion clear."
Chara said the statement was "a nice gesture. It's something that, for sure, shouldn't go that far."
He also said after the Bruins' 4-3 overtime loss to Buffalo that he will "try to reach out" to Pacioretty and talk with him by telephone or in person "when the time is right." For now, Pacioretty "probably needs time and space" to be around his family, Chara said.
Also Thursday, Air Canada told the NHL it's considering withdrawing its sponsorship unless the league tightens rules to reduce potentially serious injuries. Commissioner Gary Bettman responded that his teams could retaliate by deciding to stop using Air Canada for charter flights, an important source of revenue for the airline.
Chara did not speak at length on the investigation when he talked after the Bruins' morning skate.
"I got some media information on that this morning," he said. "But like I said, right now, I'm focusing on playing my game, and playing hockey."
Chara, who said he had no intent to hurt Pacioretty, was given a major penalty for interference and a game misconduct on the play in Boston's 4-1 loss in Montreal on Tuesday night. The Boston captain has never been suspended in his 13-year career.
The NHL said Wednesday it would not suspend Chara for slamming Pacioretty into a padded stanchion supporting a glass partition. Pacioretty, 22, was released from the hospital Thursday and was resting at home, his agent said.
Among Thursday's other developments:
• Canadiens owner Geoff Molson said in an open letter to the team's fans that "the Montreal Canadiens organization does not agree" with NHL's decision not to suspend Chara.
• In Toronto, Prime Minister Stephen Harper said the NHL, "for its own sake," should look seriously at the increase in serious injuries.
• NHL Players' Association executive director Don Fehr called for "maximizing the safety" in the area of the rink where the hit occurred and said the union would inspect the rink in Montreal "and elsewhere as needed, to make sure the appropriate padding is in place."
The league's general managers are expected to again address hits to the head at their annual meeting next week in Florida.
Pacioretty, who has 14 goals and 10 assists in 37 games, is out indefinitely.
"He has a right to be emotional and I respect that," Chara said. "I'm wishing him a fast recovery and hopefully he can be back on the ice soon and that's all we love to do. Obviously, when we go out there, we take risks. And sometimes, we do get hurt. But, it's just very unfortunate."
Bettman said in Washington, D.C., after a congressional panel discussion about encouraging youngsters to play hockey that "our hockey operations people are extraordinarily comfortable with the decision" to let Chara play.
"It was a horrific injury, we're sorry that it happened in our fast-paced, physical game, but I don't think whether or not supplemental discipline was imposed would change what happened and, in fact, the people in the game who I have heard from, almost to a person ... believe that it was handled appropriately," he said.
The league said it was "a hockey play that resulted in an injury because of the player colliding with the stanchion and then the ice surface."
Molson called news of the decision "a hard blow for both the players and fans of the Montreal Canadiens." He said Bettman had agreed to make the issue a priority at the upcoming GM meetings and added the decision "was one which shook the faith that we, as a community, have in this sport that we hold in such high regard."
The Canadiens dropped a 4-1 decision in St. Louis on Thursday night.
"You're concerned about him, but at the end of the day, we're professionals," Canadiens captain Brian Gionta said. "We're going to go out there and put things behind us. I just think our effort wasn't there tonight."
Bettman also said Pacioretty's injury is part of the game. Most concussions and head injuries this season have been from accidents or players falling rather than as the result of hits, he said.
There, indeed, has been strong debate this season over injuries from hits to the head. Pittsburgh star Sidney Crosby is among those sidelined with such an injury.
Montreal coach Jacques Martin, like Julien, will need to keep his team level headed. "Our mandate is to focus on the game," he said. "Hopefully next week, [the players] will be in better spirits."
The request for an investigation was filed by Dionne after he watched footage of Chara's hit, his spokeswoman said.
"Like all police investigations, evidence will be gathered and an investigation report will be submitted ... to see whether there's grounds for prosecution," spokeswoman Martine Berube said.
Chara was not in the starting lineup against the Sabres. But when he took the ice, and threw his first check of the night, the crowd cheered and chanted, "Cha-ra, Cha-ra" for about 20 seconds.
"I'm very thankful for that," Chara said. "It feels, for sure, great to be home."