Former Oakland Raiders quarterback Ken Stabler, the late NFL Most Valuable Player and Super Bowl winner who is a finalist for the Pro Football Hall of Fame, has been diagnosed with the brain disease CTE, Boston University researchers said Wednesday.

Stabler, who died of colon cancer at 69 in July, had Stage 3 chronic traumatic encephalopathy, Dr. Ann McKee told the Associated Press. McKee said the disease was widespread throughout his brain, with “quite severe” damage to the regions involving learning, memory and regulation of emotion.

“We've now found CTE in former NFL players who played every position except kicker,” said McKee, a professor of neurology at Boston University. “While we know on average that certain positions experience more repetitive head impacts and are more likely at greater risk for CTE, no position is immune.”

The diagnosis was first reported by The New York Times.

The disease, which can be diagnosed only after death, is linked to repeated brain trauma and associated with symptoms such as memory loss, depression and progressive dementia. CTE has been found in the brains of dozens of former football players.

According to Chris Nowinski, the founder of the Concussion Legacy Foundation, Stabler told his family he wanted to have his brain studied after learning that former NFL linebacker Junior Seau had been diagnosed with the disease. In 2012, Seau shot himself in the chest at the age of 43.

“What is interesting about Ken Stabler is that he anticipated his diagnosis years in advance,” Nowinski wrote in an email to the AP. “And even though he's a football icon, he began actively distancing himself from [the] game in his final years, expressing hope that his grandsons would choose not to play.”

McKee said the extent of the damage to Stabler's brain was surprising because he was relatively young when he died and because he was a quarterback and thought to be less exposed to repeated head trauma.

“There was no evidence of any other brain disorder to explain the difficulties he experienced during life,” McKee said.

The left-handed Stabler, nicknamed “Snake” for his ability to escape from defenders, led Alabama to an undefeated season in 1966. A second-round draft pick by Oakland, he was the NFL's Most Valuable Player in 1974 and led the Raiders to victory in the 1977 Super Bowl.

In all, Stabler threw for 27,938 career yards and had a .661 winning percentage over 15 seasons, which also included stints with the Houston Oilers and New Orleans Saints. He was selected as a finalist for the Hall of Fame by its Seniors Committee; the inductees will be announced Saturday.

Denver Broncos linebacker Brandon Marshall said at a Super Bowl availability Wednesday that the news bothers him.

“You've got to look after yourself because, really, nobody else will,” he said, adding that he has heard about players walking away from the game but can't do it himself.

“The game is so much a part of who I am, so I can't give up a big part of me. I just hope the game doesn't one day take away a big part of me,” he said. “I mean, Lord willing it doesn't happen, but say something does happen, I don't think I'm going to regret it because I'll say, ‘I did what I wanted to do.'?”

Security update: NFL security leaders and top law enforcement officials say there is “no credible threat” to Super Bowl 50.

Jeffrey Miller, NFL senior vice president of security, planned to walk the perimeter of Levi's Stadium again Wednesday and he estimates it's approximately 3 to 4 miles around the facility in Santa Clara, Calif., where Sunday's Super Bowl will be played between the Carolina Panthers and the Broncos.

Miller said he is satisfied with the collaborative effort between local, state and federal law enforcement agencies to handle any possible issues, including terrorism of any kind.

“It gives the NFL a great deal of confidence in the safety of our premier event, our teams and our fans,” Miller said at a news conference Wednesday. “I can speak for Commissioner [Roger] Goodell in saying that we are deeply appreciative of the leadership, resources and attention to detail put forth by our public safety partners.”

Still an expensive seat: As gameday gets closer, ticket prices for the Super Bowl on the secondary market are dropping.

The average ticket price sold on StubHub is down from $5,037 on Tuesday to $4,936 on Wednesday. The cheapest ticket available for the game at Levi's Stadium has fallen from $3,090 to $2,805.

Prices are higher than the past two years. The average ticket to last year's game in Arizona between the New England Patriots and the Seattle Seahawks went for $4,222, with prices the previous year for the game in New Jersey between Denver and Seattle going for $2,516.

More than a quarter of the tickets sold for this year's game, 27 percent, have been to buyers from California. Fans from the states of the two teams are next up, with 10 percent of ticket buyers from North Carolina and 9 percent from Colorado.

Broncos' Murphy questioned in sting: Denver coach Gary Kubiak says he's disappointed he had to send home one of his practice squad players who was caught up in a prostitution sting a few miles from the team hotel.

The Broncos sent safety Ryan Murphy home after he was questioned by authorities during a sting in San Jose, Calif., on Tuesday.

Santa Clara County Sheriff's Sgt. James Jensen said Murphy, 23, was detained and questioned Tuesday and released after investigators determined he was not involved in any criminal activities.

Father of Broncos D-lineman dies: Broncos defensive lineman Antonio Smith plans to play in the Super Bowl despite learning of his father's death Wednesday.

Team spokesman Patrick Smyth told the Associated Press that there are no plans for Smith to leave the team.

Smith told the Denver Post he learned of his father's death Wednesday in a phone call from his mother.

Marty Christopher Williams, 55, who had been incarcerated for more than 20 years, had recently undergone heart surgery, Smith told the newspaper.

Smith, 34, is a 12-year NFL veteran who joined the Broncos this season after his release by the Oakland Raiders. A key member of the league's top defense, he posted 21/2 sacks in the regular season and another in the playoffs.