DENVER -- Denver Zoo officials said a man who died while resisting police Monday claimed he was a lion and aggressively attacked zoo security officers.

Police and zoo officials said Alonzo Ashley, 29, was attacking others, and zoo security was forced to call police to report a domestic violence incident because the man was shouting and knocking over garbage cans and his girlfriend appeared frightened.

Police said Ashley stopped breathing as they physically restrained him on the ground. He died later at a hospital.

Ashley's girlfriend has confirmed the man was upset and offering to fight zoo security officers, but she also told 7NEWS that Ashley appeared to be suffering from heat distress on a hot day. She said he was trying to cool off his head under a drinking fountain when a security guard told him to stop.

At a Thursday afternoon news briefing, zoo officials called the death an "unprecedented tragedy" and said security officers acted only to protect zoo visitors and the girlfriend.

"It's been a very difficult week for Denver Zoo and everyone involved in the tragedy that occurred here on July 18th," Denver Zoo President and CEO Craig Piper said. "I would like to offer our sympathy to the family and friends of Mr. Ashley."

"I want to begin by expressing my gratitude to our security team that works diligently to protect the safety of guests, staff and animals," Piper said, repeatedly lauding security officers' "dedication to ensuring that the Denver Zoo is a safe place for all."

Civil Rights Activists To Protest At Zoo Friday

Civil rights activists plan to hand the Denver Zoo CEO a list of demands Friday afternoon.

Alvertis Simmons told 7NEWS the march will begin at 2 p.m. near the Museum of Nature and Science near Colorado and Montview Boulevards. Protestors will deliver a list of at least five demands to the zoo. Simmons would not reveal what those demands would be Thursday night. He did say he wants to make sure the police investigation into Ashley's death doesn't take up to a year like the investigation into the death of Marvin Booker.

Booker died July 9, 2010, while being restrained by deputies at the Denver County jail. The circumstances surrounding his death weren't revealed until the internal investigation was complete 10 months later.

Zoo: Man Clamed He Was A Lion

Zoo spokeswoman Tiffany Barnhart said the incident began just before 5 p.m. Monday when a zoo staffer radioed security "that a man appeared to be passed out near the elephant exhibit."

A senior security officer responded and "found Mr. Ashley standing with his head under the drinking fountain," Barnhart said.

"Concerned for the well-being of Mr. Ashley on this hot day, our security officer approached him and asked if he was OK," she said. "He asked this several times and got no response."

"Mr. Ashley then began making irrational statements to the security officer," she added.

"Mr. Ashley claimed several times that he was lion," Barnhart said.

The security officer spoke with a woman nearby who said she was Ashley's girlfriend.

Suddenly, Ashley began yelling at the girlfriend and knocking over trash cans, Barnhart said.

Concerned for the woman's safety, the security officer backed off and called a supervisor, Barnhart said.

Security staffers decided to call police. But as the security officer called 911, Barnhart said Ashley ran after the security officer.

"Mr. Ashley chased our security officer, tackled him to the ground and began punching him," said Barnhart. "During the incident our security was beaten and suffered several scratches and bruises."

Girlfriend Told KHOW Radio Ashley Ran After Security

During an appearance on a KHOW-AM radio program Tuesday morning, Ashley's girlfriend, Elaina, described seeing her boyfriend go after the security officer.

"The security stepped out from behind the bushes. That's when my boyfriend was like, 'I'm going to get him.' And that's when he told me to just sit at the bench," Elaina told KHOW-AM. "He started running toward the security."

She said she did not see what happened after he ran off.

"And that's when he came back with cuts on his hands and cuts on his knees," Elaina told KHOW-AM.

Police have said that Ashley spun out of control, hitting one police officer and biting another. Police said a zoo employee was also bitten and suffered a head injury.

"We believe that this is an isolated incident that is certainly unprecedented," Barnhart said. "In our entire zoo history, we've never experienced anything like this."

Piper noted, "We've experienced an outpouring of kindness and support for the zoo as a beloved family destination."

Barnhart added that calls and emails to the zoo have been largely supportive.

"Unusual" For Family Representative To Watch Autopsy

Ashley's autopsy on Wednesday did not reveal the cause of death. It could be weeks before additional testing provides new information.

7NEWS learned about an unusual situation at the autopsy.

Don Bell, chief investigator with the medical examiner's office confirms a woman observed the autopsy on behalf of the Ashley family attorney.

"It's unusual, but we feel it's the best thing to allow it to be fair to both sides," said Bell. "We owe it to both sides to allow them to view the collection of evidence."

Bell said members of the police department routinely observe the autopsy during an investigation.

He said it has been five or six years, if not longer, since an outside representative observed an autopsy. Bell said the Chief Medical Examiner must approve the request.

Ashley Family Attorney Explains Autopsy Observation

"We always try to eliminate the what-ifs," said Ashley family attorney Will Frankfurt.

7NEWS asked Frankfurt if there was a concern about any funny business with the authorities conducting the autopsy.

"No," said Frankfurt. "We knew that if we didn't have a set of eyes in the room, and something happened or we saw something in the autopsy report, that we couldn't go back in time and say this was or was not done."

When asked if there was any reason to believe police did not follow proper protocol, Frankfurt explained his fact-finding is still in the early stages.

"We're still looking into that, but again, there are two sides to the story," said Frankfurt.