CLEVELAND -- Angered and betrayed by LeBron James' decision to leave for Miami, Cavaliers owner Dan Gilbert accused the NBA's MVP of quitting during the playoffs.

Gilbert, who posted a letter to Cavs fans on the team's website shortly after James announced his plans to sign with the Heat, told The Associated Press late Thursday night that it's "accountability time" for James.

"He has gotten a free pass," Gilbert said in a phone interview with The AP. "People have covered up for [James] for way too long. Tonight we saw who he really is."

“Gilbert It's not about him leaving. It's the disrespect. It's time for people to hold these athletes accountable for their actions. Is this the way you raise your children? I've been holding this all in for a long time.
” -- Cleveland Cavaliers owner Dan Gilbert

Gilbert said James quit on the Cavs during their second-round series against the Boston Celtics, who rallied from a 2-1 deficit to eliminate Cleveland.

"He quit," Gilbert said. "Not just in Game 5, but in Games 2, 4 and 6. Watch the tape. The Boston series was unlike anything in the history of sports for a superstar."

The Cavaliers were beaten by 32 points in Game 5. During the game, James appeared distracted and uninterested, often glaring at Cleveland's coaches as the Cavs tried to foul to get back into the game in the second half. James also made some puzzling postgame comments, saying he had "spoiled" people with his play over seven seasons.

Gilbert also said he believes James quit on the Cavs in Game 6 of their series in 2009 against Orlando.

"Go back and look at the tape," he said. "How many shots did he take?"

The NBA will not comment on Gilbert's statement, league spokesman Tim Frank told ESPN The Magazine's Chris Broussard.

Gilbert, who has owned the Cavs for five years, said he was most disappointed by James' behavior in the months leading up to the superstar's announcement that he is going to Miami to play with Dwyane Wade and Chris Bosh. Gilbert said James never returned a single phone message or text since the end of the season and that the Cavs were not informed of James' decision until he went on the air.

Gilbert said Rich Paul, one of James' business partners, called the Cavs moments before the announcement.

"LeBron James needs to go to another team with two superstars already so he can win a championship," Gilbert said. "We will win a championship before [the Heat] do."

Gilbert said he now wishes he had done some things differently with James, who spent seven seasons with the Cavs.

"It's not about him leaving," Gilbert said. "It's the disrespect. It's time for people to hold these athletes accountable for their actions. Is this the way you raise your children? I've been holding this all in for a long time."

In Miami, Wade said he was stunned by Gilbert's comments.

"I think I'm happy that I have the owner that I have here in Miami," Wade told The Associated Press late Thursday night. "I'm happy Micky Arison is my owner. I couldn't believe it. I'm speechless. It's very unfortunate and I think it makes LeBron that much better about his decision.

"We knew 'Bron would take some backlash," Wade added in his interview with AP. "I told him he's a strong man for it."

In the letter posted on the Cavaliers' website Gilbert called the process on James' free agency "narcissistic, self-promotional build-up culminating with a national TV special of his 'decision' unlike anything ever 'witnessed' in the history of sports and probably the history of entertainment."

Gilbert told Cavs fans: "You simply don't deserve this kind of cowardly betrayal.

"I PERSONALLY GUARANTEE THAT THE CLEVELAND CAVALIERS WILL WIN AN NBA CHAMPIONSHIP BEFORE THE SELF-TITLED FORMER 'KING' WINS ONE"

Gilbert promised that "curse" on Cleveland sports would follow James to Miami.

"The self-declared former 'King' will be taking the 'curse' with him down south," Gilbert wrote. "And until he does 'right' by Cleveland and Ohio, James [and the town where he plays] will unfortunately own this dreaded spell and bad karma."

Gilbert finished the letter by promising to put his focus on bringing a championship to Cleveland with the Cavaliers.

"I PROMISE you that our energy, focus, capital, knowledge and experience will be directed at one thing and one thing only:

"DELIVERING YOU the championship you have long deserved and is long overdue...."

The Associated Press contributed to this report.