Details of the gruesome rape that prosecutors say left a Somerville High freshman soccer player bleeding badly on the floor of a bathroom at a school-sponsored sports camp — allegedly with a broomstick brandished by three junior varsity teammates — have left parents stunned and shocked.

“I stand with everybody in the community in being horrified and outraged about what allegedly occurred,” said Ken Brociner, whose son Marcelo is a co-captain of the team and has known one of the defendants, 17-year-old Galileo Mondol, since he was 6. “I’ve known (Mondol) to be a sweet and gentle kid. I certainly don’t want the kids to go to jail for 20 years. They allegedly did some terrible things, but they’re kids.”

Mondol and two 16-year-old male players whose names authorities have not released were arraigned yesterday. Mondol, who will remain behind bars in the Berkshires pending a dangerousness hearing Friday, is charged with aggravated rape and assault with intent to rape, and prosecutors say the juveniles face “similar charges” in the alleged Aug. 25 assault at Camp Lenox, a 170-acre retreat for kids ages 7 to 16 in Lee. Their court proceedings were not public.

Prosecutor Rachael T. Eramo said Mondol and the juveniles “were laughing after the assault occurred,” and that Mondol threatened one boy who said he was going to report them, saying, “You better keep your mouth shut.”

Eramo said Mondol and the juveniles entered the freshman cabin and announced: “We’re going to pick someone. It’s you, no it’s you, no it’s you,” before grabbing one boy and forcing him to his hands and knees. Mondol, upon seeing the broom, initially told the other two to stop, Eramo said, but he later chimed in, “I want to have a crack at that.”

Two of the victim’s fellow freshmen fought off the assault, Eramo said. “Both of them were able to keep their pants on,” Eramo said.

Eramo said investigators have collected a bloody tissue and a brown stain from the cabin’s bathroom floor. She said the boy who was raped bled badly.

Mondol’s lawyer, William Korman, said his client “was in the wrong place at the wrong time.” Korman told reporters later that his client tried to stop the attack.

“He was in the cabin and when he saw what was about to occur, he said to the two co-defendants, ‘Don’t do this!’ And that’s out of the victim’s mouth,” Korman said. “It’s the victim himself who said my client did everything he could to stop this assault.”