The windmilling fists and stomping feet rain down blows on the 13-year-old boy.
Trapped on the floor between the bus seats, he cries out as he receives fierce punch after vicious kick from the three bigger, older youths.
As the relentless assault unfolds, the driver of the Florida school bus alerts the dispatcher, pleading for aid. But he doesn't physically step in to help.
The bus driver, at least according to his school's policy, did nothing wrong.
The attack took place July 9 in Pinellas County, Florida. But the horrific cell phone video -- and the surveillance video -- came out only recently.
As the boy is pummeled, the bus driver, John Moody, yells at the assailants to leave the boy alone.
He also asks dispatchers to send help.
"You gotta get somebody here quick, quick, quick, quick," he says. "They're about to beat this boy to death over here."
"Please get somebody here quick. There's still doing it," he adds. "There's nothing I can do."
'Like a bad dream'
Moody, 64, said on CNN's Piers Morgan Live that he was calling for help on his radio, as school policy required.
"Me jumping in the middle of that fight with three boys, it would have been more dangerous for other students on the bus for as myself," he said. "There's just no telling what might have happened."
Earlier, he told CNN affiliate WFLA he was "in shock" and "petrified." And he told CNN that watching the video is "like a bad dream."
"I took it really personal. I had many sleepless nights. I had nightmares," he said.
Moody retired two weeks after the attack, after 18 years driving buses. The fight was "the final straw -- and it was a big straw, too," he said.
Police say the youths attacked the 13-year-old after he told officials at their dropout prevention school that one of them had tried to sell him drugs. The ferocity of the attack left the victim with two black eyes and a broken arm.
Criticism, but no basis for charges
Gulfport Police Chief Robert Vincent told WFLA that Moody should have stepped in.
"There was clearly an opportunity for him to intervene and or check on the welfare of the children or the child in this case, and he didn't make any effort to do so," Vincent said.
But prosecutors say they have no grounds on which to bring charges.
"It wasn't like he was looking out the window cleaning his fingernails or something like that," said Chief Assistant State Attorney Bruce Bartlett, according to CNN affiliate WFLA.
According to Pinellas County school policy, the bus driver isn't required to intervene, only to call dispatch. He can step in, if he feels it's safe.
Police said Moody could have given first aid to the victim after the attackers jumped off the bus, but Bartlett said the 13-year-old didn't hang around.
"The kid gets up and skedaddles out the door," he said.
Other counties actually forbid drivers from physically stopping fights.