The preliminary results of an autopsy on a New England Patriots fan who died after a "scuffle" at a game Sunday "did not suggest traumatic injury, but did identify a medical issue," the Norfolk district attorney said in a statement.

Dale Mooney, 53, collapsed at Gillette Stadium in Massachusetts on Sunday night after an incident during the fourth quarter of the Patriots game against the Miami Dolphins. He was taken to a hospital and pronounced dead just before midnight, authorities said.

While the district attorney referred to the incident involving Mooney as a "scuffle," one fan said it was a "violent confrontation." The investigation into Mooney's death remains open and ongoing, according to the DA's office.

"Our investigation has included numerous law enforcement interviews and the examination of multiple angles of video capturing the scuffle prior to Mr. Dale Mooney's collapse during the Sunday night game at Gillette Stadium," the DA's office said in a statement Wednesday.

"Preliminary autopsy results did not suggest traumatic injury, but did identify a medical issue. Cause and manner of death remain undetermined pending further testing," the statement said.

The statement comes amid questions about what happened before Mooney's collapse and death.

Joseph Kilmartin, a Patriots fan who was at the game, told CNN affiliate WCVB he witnessed a "violent confrontation" leading up to the fan's death. He said he witnessed Mooney approach a group of fans on the 300-level of the stadium toward the end of the fourth quarter.

"He basically grabbed another fan," Kilmartin told WCVB. "They started tussling around for a few minutes. At one point, another fan walked over. He punched him ... and the man just went out. It was pretty hard to watch," Kilmartin said.

Kilmartin declined CNN's request for an interview.

The Patriots released a statement identifying Mooney as a longtime fan and season ticket holder.

"We are heartbroken to learn of the tragic passing of Dale Mooney, a lifelong Patriots fans and 30-year season ticket member, who died while attending last Sunday night's Patriots game," Gillette Stadium officials said in a statement. "We continue to work with local authorities to assist them with their ongoing investigation. We extend our sincerest sympathies and heartfelt condolences to Dale's family and to all those who are mourning his loss."

Mooney's wife, Lisa, told WCVB that her husband, a season ticket holder for 30 years and father of two, went to Gillette Stadium with three friends who later told her they were "verbally taunted" by other fans during the game.

"It takes a lot to get him mad," Lisa Mooney said. "He has the patience of a saint. I don't know what happened."

According to Lisa Mooney, her husband had no known medical condition that she was aware of. "I want to know what happened," Lisa Mooney told WCVB. "What caused this?"

CNN has been unable to reach Lisa Mooney for comment.