FORT LAUDERDALE, Fla. - Police say they will seek murder charges against the attackers who beat a homeless man to death and are suspected in two similar attacks a few hours later.

The first attack was caught on a university surveillance video before dawn Thursday, prompting a police search for two to four young men. The crime, though unusual for being captured on videotape, is remarkably common, advocates for the homeless say.

Norris Gaynor, 45, was attacked later as he slept near the Broward Center for Performing Arts and died from his injuries at a hospital Thursday, police said. The other victims, both hospitalized in serious condition, have not been identified.

The video from Florida Atlantic University shows two men chasing and beating a man who had been sleeping on a bench. It looked like they were going for the head, Detective Katherine Collins said.

The Fort Lauderdale Sun-Sentinel reported that as the two teens ran off, headlights from a car or truck could be seen shining westward on the scene on Las Olas Boulevard. Authorities said Thursday they were looking for a white van with no markings.

The 58-year-old man found a security guard, who called for help, and the victim was hospitalized with head trauma and defensive fractures, authorities said.

Gaynor was beaten about 90 minutes later in a chillingly similar attack. He had been sleeping on a secluded park bench near the performing arts center, police said.

Another 90 minutes after that, a third homeless man flagged down a fire crew passing a church and said he had been attacked while he slept.

Its senseless. If you look at these kids, it was almost like it was fun and games for them, police Officer Scott Russell said.

NBC reported that the Salvation Army was opening an emergency shelters for the homeless in Fort Lauderdale, something the group usually does only on extremely cold nights.

Four teenagers pleaded guilty last month to fatally beating a 53-year-old homeless man in Daytona Beach in May. They await sentencing next month. A fifth teen still faces an aggravated battery charge and is free on bail.

What made Friday's crime unusual, advocates for the homeless said, wasn't that it was committed, but that it was captured on videotape.

'Tip of the iceberg'
The nonprofit National Coalition for the Homeless says that there were more than 398 acts of violence against homeless people in the last six years, of which about 156 resulted in death. These statistics do not include reports of sexual assault against homeless women.

"We think it's the tip of the iceberg," said Michael O'Neill, coordinator of the coalition's Homeless Speakers Series, designed to educate people on the causes of homelessness.

In a report on hate crimes against the homeless published in mid-2005, the organization said it believes many cases go unreported or unpublicized because many homeless people are mentally ill or addicts, fear retaliation or are frustrated with the police. As a result, the report says, it is difficult to assess the true magnitude of the problem.

O'Neill told there was an escalation in violence against homeless people after two young men produced a series of movies, starting with "Bum Fights" in 2001 in which they filmed homeless people they had persuaded to do humiliating and dangerous things in exchange for drugs, small change or food. The video producers at first faced seven felony counts and four misdemeanor charges in connection with production of the videos, but ultimately were sentenced to 250 hours of community service.

"There's been a lot of copycat crimes," O'Neill said.

In an interview with the Sun-Sentinel, a Fort Lauderdale advocate for the homeless said beating homeless people is quite common in the area.

"It's one of the shameful secrets we have, the beating of homeless for sport," said Marti Forman, CEO of the Cooperative Feeding Program, told the newspaper. "It's a recreation thing, it's an initiation for gangs and fraternities."

She said she hoped the fact that the brutality was videotaped would generate outrage.

The Associated Press and NBC News contributed to this report.