MIAMI â€"  It is being called one of this city's goriest crimes: A naked man was on top of another nude man along a busy highway, biting into the man's face, tearing it to pieces. A police officer arrived to help, but the mauler growled at him and continued to chew away, stopping only when he was shot to death.

Miami police said little Tuesday about the attack, which took place Saturday afternoon in the shadow of The Miami Herald headquarters. Surveillance video from the newspaper's security camera showed cars, motorcycles, pedestrians and bicyclists passing by.

The victim, identified as 65-year-old Ronald Poppo, a homeless man who lived under the causeway, was in critical condition.

"He had his face eaten down to his goatee. The forehead was just bone. No nose, no mouth," said Sgt. Armando Aguilar, president of the Miami Fraternal Order of Police. "In my opinion, he just happened to be in the wrong place at the wrong time."

Sgt. Javier Ortiz, vice president of the Miami Fraternal Order of Police, said it was one of the bloodiest "and goriest scenes I've ever been to."

"It was not only grotesque, it was just very sad, the amount of blood. It was very sad to see what happened to this gentleman that had his face eaten," Ortiz said.

It's not clear what led Rudy Eugene, 31, to attack Poppo. Eugene's ex-wife, Jenny Ductant, told WPLG-TV, said he was somewhat paranoid.

"I wouldn't say he had mental problem but he always felt like people was against him ... No one was for him, everyone was against him," she told the station. She and Eugene's mother declined comment when reached by The Associated Press.

Larry Vega was riding his bicycle off the causeway, which connects downtown Miami with Miami Beach, when he saw the attack.

"The guy was, like, tearing him to pieces with his mouth, so I told him, `Get off!"' Vega told Miami television station WSVN (http://bit.ly/L6kwWt). "The guy just kept eating the other guy away, like, ripping his skin."

Vega flagged down the Miami police officer, who can be seen exiting his car on the Herald video. Vega said the officer repeatedly ordered the attacker to get off. Eugene just picked his head up and growled at the officer before continuing to maul his victim, Vega said.

The officer shot Eugene, but he just kept chewing, Vega said. The officer fired again, killing Eugene.

Vega refused to comment when reached by The Associated Press, saying he wanted to put what he witnessed behind him.

Detective William Moreno would not release details about the shooting, citing the ongoing investigation. The Miami-Dade County medical examiner declined to provide any information until after the autopsy, which was scheduled for Tuesday. Police have not released details from the autopsy and it could be weeks before the results of toxicology tests are available.

Ortiz said the officer, who is part of a crisis intervention team and trained to deal with the mentally ill, had no choice but to fire.

"He's clearly shaken up," Ortiz said, adding that the officer had been administratively reassigned pending an investigation, as is standard after an officer-involved shooting.

After the shooting, the Herald's video zooms in on the scene. Most of it is blocked by an overpass, but two sets of uncovered legs can be seen. One set never moves, while the other twists and turns as if the person is in pain.

"It was just a blob of blood," Vega said. "You couldn't really see, it was just blood all over the place."

Court records show that Poppo has several arrests for public intoxication.

According to Miami-Dade court records, Eugene had been arrested for multiple misdemeanors, mostly marijuana-related charges. The most recent arrest was in 2009. The Herald reported that he played football at a Miami area high school in the late 1990s.

Ives Eugene, who identified himself as Rudy Eugene's uncle, described his nephew as a "nice and hard-working" man who washed cars at a local dealership.

He said his nephew had asked his girlfriend to borrow her car, but she said no. "So he rode the bicycle, and he never came back home," he said.