Denver police are reviewing surveillance footage from Sports Authority Field at Mile High for any trace of Paul Kitterman, the 53-year-old man who disappeared last Thursday during the Broncos game against the San Diego Chargers, reports said. The search for Kitterman is being treated as an “active missing person’s investigation,” Denver police spokesman Sonny Jackson told CNN.

“We don’t know if he voluntarily walked away,” Jackson said. “We don’t specifically see any foul play … but the fact is we are not ruling out anything.”

Authorities have yet to locate Kitterman in hundreds of hours of security footage. A witness claims to have seen him during the third quarter of the Broncos-Chargers game, but his location within the stadium could not be confirmed, KUSA-TV, Denver, reported. Denver police tweeted Tuesday officers were investigating a body near Sports Authority Field, but the victim was not believed to be Kitterman.

"The surveillance video that we're looking at, [what we're] looking for is to see when he was last seen at the stadium, who he might have been with, just his demeanor the last time he was seen," Jackson told KUSA. "That might tell us a lot."

A native of Kremmling, Colorado, Kitterman attended the Broncos game stepson Jarod Tonneson, family friend Tia Bakke and Bakke's boyfriend. Tonneson got up from his seat at halftime to use the bathroom. When he returned, Kitterman was gone. Frantic searches of the stadium’s interior and exterior, as well as calls to local hospitals and jails failed to yield any results.

Kitterman has no history of substance abuse or any known medical conditions. He does not carry a cell phone and reportedly had about $50 in cash on him at the time of his disappearance.

“It just doesn’t feel like something good happened,” Tonneson said. “I want him to know that we’re worried about him. I just want him to call and let us know he’s OK.”

Police told Bakke they believe Kitterman simply decided to leave the stadium, but she suspects foul play. “Paul did not just walk away on his own,” she said. “Something bad has happened to him.”