KANSAS CITY, Mo. -- The manager of Randie Carver's opponent in Sunday's fatal fight raised questions Wednesday about a potential conflict of interest involving Carver's ties to the referee.

Referee Ross Strada, who has acknowledged a close friendship with Carver, has been criticized for not stopping the fight soon enough.

"He should have stopped the fight. It's that simple," said Scott Massoud, the Brooklyn, N.Y.-based manager of Kabary Salem, who knocked out Carver in the 10th round of Sunday's 12-round North American Boxing Federation title fight.

Carver, 24, died Tuesday, two days after emergency brain surgery. An official cause of death has been determined, but relatives requested the information not be disclosed.

Carver, who was repeatedly head-butted in the early rounds of the fight, fell sluggishly to the canvas in the 10th round after taking an overhand right and a straight left from Salem. He tried on four occasions to stand up, but could not even get to his knees.

After Strada ruled a knockout, Carver's eyes appeared to roll back in his head and he lost consciousness. He was rushed to the hospital after paramedics worked on him for about 20 minutes in the ring, but he never appeared to regain consciousness.

Carver's supporters were upset by the head butts. Salem was penalized twice in the early rounds for holding, but was not warned about head-butting.

Officials with Missouri's Office of Athletics -- which oversees boxing in the state and licenses referees -- have found "no cause for disciplining the fighters, the referee, the promoter or the matchmakers," said Jim Gardner, a spokesman for the state's Department of Economic Development, which oversees the athletics office.

Strada, whose phone number is unlisted and could not be reached Wednesday, has disputed the number of head butts in the fight and said if there had been something excessive, he would have stopped the bout.

Earlier, Strada said Carver looked exhausted in the middle rounds. In the eighth round, Carver looked noticeably tired and had a hard time getting off the ropes when Salem pushed him.

"There weren't 20 hard punches thrown in the fight," Strada said Monday. "I've never seen Randie that physically out of shape. But I can't call a fight because a fighter is tired. That's the job of (the fighter's) corner."

Massoud, who said Salem has been crying and praying since the news of Carver's death, said Carver's friendship with Strada created a dangerous conflict of interest. Had he known of the friendship before the fight, Massoud said he "would have been a little more boisterous" in trying to stop the bout.

"If he had stopped the fight and Randie lost, due to the stoppage, he would have been blamed for his loss," Massoud said. "And that's something the referee didn't want. I'm not bad-mouthing (Strada), but we could've been out of there a lot sooner."

Strada's claims that Carver appeared tired were underscored by the fact that he had fought seven bouts in the last 11 months.

Before Sunday's fight, Carver had fought twice since winning the NABF supermiddleweight title in a 12-round decision May 23. His record was 23-0-1 before the bout.

NABF president Sam Macias said the federation would work with any investigation by state regulators.

Macias, whose group brought two outside judges to Sunday's bout because the fight was held in Carver's home area, said it is up to the state's Office of Athletics to pick referees.

It is not unusual, Macias said, for referees to handle bouts involving friends.

"If you're boxing in a hometown, with gyms being where refs will go to keep their skills up and referee sparring matches, they become friends," Macias said. "I don't think it affects their judgment."

Frank Brancato, a lawyer with a Kansas City firm representing Carver's family, refused to comment Wednesday except to say his firm was preparing for an initial investigation into the case.

A spokeswoman for Harrah's North Kansas City Casino, which hosted Sunday's televised fight, said the casino was reevaluating its plans to hold future bouts.