In one of the attacks, captured on a university surveillance tape, two young men with baseball bats repeatedly hit the victim as he lay on a sidewalk and tried to block the blows with his hands. In the other attacks, authorities said the assailants used a paintball gun, bats and a golf club.
The videotaped attack sparked public outrage and helped lead authorities to the teens.
Brian Hooks and William Ammons, both 18, and 17-year-old Thomas Daugherty were indicted earlier this month on murder charges in the killing of 45-year-old Norris Gaynor and on attempted murder in the beatings of Raymond Perez and Jacques Pierre.
Gaynor was beaten with a baseball bat while he slept on a park bench Jan. 12. He was also shot with a paintball gun.
Perez was assaulted with a golf club outside a nearby church, and Pierre was bludgeoned with a bat on the Fort Lauderdale campus of Florida Atlantic University, the attack caught on tape.
In court, the teens' attorneys described each youth as contrite and upset about what had happened.
"He's got the weight of the world on his shoulders," said Daugherty's attorney, Michael Gottlieb. "He definitely feels bad."
Hooks' lawyer, Jeremy Kroll, said his client was "obviously disturbed by what happened" and that evidence would show Hooks was present but did not actively take part in the beatings.
One witness who testified before a grand jury identified only Hooks and Daugherty — the two teenagers seen in the videotaped beating — as taking part in the fatal attack on Gaynor, their lawyers said. Michael Rothschild, the assistant public defender representing Ammons, said that witness could be key to his client's defense.
"He wasn't with them when Mr. Gaynor was unfortunately killed," Rothschild said of the witness's testimony.
Police reports, however, allege that Ammons fired paintball slugs at Gaynor while Daugherty struck him on the head with a baseball bat.
Under Florida law, people who take part in a crime can be charged with murder if someone is slain, even if they didn't commit the actual killing.
Hooks, of Plantation, and Ammons, of Fort Lauderdale, could face the death penalty if convicted; Daugherty, also of Plantation, is being tried as an adult but faces a maximum sentence of life in prison because of his age.
Prosecutors have not said if they will seek the death penalty. Circuit Court Judge Cynthia Imperato set a March 31 hearing.
Police also are investigating whether the teens may have been involved in five other assaults on homeless people who came forward after the Jan. 12 attacks.