The shirtless 15-year-old screams as he lies facedown on the kitchen floor of his Tucson group home. He has no arms or legs, so he can’t flee or fight back. But a sheriff’s deputy at least twice his size is crouching over him and pinning him to the ground, using his body weight to restrain the quadruple amputee.

The eight-minute cellphone video, which was first published by KOLD, has now prompted an internal affairs investigation at the Pima County Sheriff’s Department. A spokesman told The Washington Post on Friday that the deputy in the video, Manuel Van Santen, has been placed on administrative leave.

But Pima County Public Defender Joel Feinman told The Washington Post that the disturbing incident likely wouldn’t have come to light if it weren’t for another teenager at the group home, who recorded the confrontation and then had his head pushed into the wall by deputies.

“These are kids who have already been traumatized in some way,” said Feinman, whose office is representing both boys. If a parent reacted to their teenager acting up in the same way the deputy did, he added, “they might be arrested for child abuse.”

While most information about the teens is being withheld to protect their privacy, Feinman said that Immanuel, the 15-year-old quadruple amputee, is in state custody because he was abandoned by his parents. On the morning of Sept. 26, an adult who works at the group home called police to report that Immanuel had knocked over a trash can and was yelling and screaming. Feinman isn’t sure what got the teenager riled up, and, in his opinion, it doesn’t matter.

“Fifteen-year-olds who have not been through what Immanuel went through act out all the time,” he pointed out.

The deputy from the Pima County Sheriff’s Department who responded to the call determined that Immanuel was disturbing the peace and decided to restrain him, Feinman said. That’s when C.J., a 16-year-old who also lives at the group home, began surreptitiously recording from an adjoining room.

At the video’s start, a white deputy in wraparound sunglasses can be seen kneeling on the ground and holding the black teenager in a headlock. Immanuel grows increasingly upset, his voice rising to a frantic shriek as he tells the officer not to hold him down.

When the deputy loosens his grip, Immanuel tries to shake him off and break free, but he doesn’t get far. The officer tackles him, wrapping his arms around the teenager and practically lying on top of him as he wrestles him to the floor. An uncomfortable minute passes as the quadruple amputee swears and screams at the deputy, who uses one forearm to hold him pressed to the ground.

Eventually, Immanuel stops protesting and the officer lets him get up, asking him what his problem is, and why he kept moving when he was told not to move. As the 15-year-old insists he doesn’t have a problem, the cop gets louder, bending over so that his face is inches away from the teenager’s.

“I will raise my voice to you whenever the [expletive] I want, you understand?” the officer yells.

C.J., who has been recording the scene as he eats his breakfast in the next room, interrupts. “Hey, you asked him a question, and he answered,” he tells the deputy.

“Shut the hell up!” the cop snaps back. He tells the 16-year-old to go to his room; C.J. responds that he’s eating his cereal and isn’t allowed to be in his room. The deputy storms over, screaming at C.J. and telling him to stay out of something that doesn’t involve him. “You shut the hell up!” he yells again. C.J. tells him to get out of his face.

“You’re going to get arrested, too,” the cop says.

A third teenager takes the phone and begins filming as C.J. is turned around and placed in handcuffs. Without warning, the deputy slams the head of the unsuspecting 16-year-old into the wall. There’s a loud crash, and then the black teen is led to a squad car by the two officers, who appear to be white.

Both C.J. and Immanuel were jailed for disorderly conduct, Feinman said. The deputy hadn’t been wearing a body camera, but when C.J. met with his attorney from the public defender’s office, he suggested watching the video he had captured before his arrest.

“We did, and it was horrific,” Feinman said. He cried the first time he watched the footage, he said, as did many of his colleagues. “We’re public defenders, so we have an iron stomach for a lot of things, but this was especially terrible.”

Given that Immanuel has no legs and is missing most of his arms — and wasn’t even wearing a shirt, making it unlikely that he could have somehow been hiding a concealed weapon — Feinman questions how he could have posed a threat to “this very large policeman with a badge and a gun.” Regardless of what the teenager said to the officer, he argues, the better response would have been to sit down and try to de-escalate the situation.

The Pima County Sheriff’s Department told KOLD that they hadn’t previously been aware of the video and would launch an investigation. In an email to The Post, a spokesman identified Van Santen as an 11-year veteran of the force.

A spokesman from the Pima County Attorney’s Office told The Post that they, too, first saw the video on Thursday. Only one of the teenagers — identified by KOLD as Immanuel — faced charges after the incident, according to prosecutors. Those have now been dropped.

“These are kids who live in a group home because they can’t live with their parents,” Feinman said. “This is exactly the type of person that law enforcement needs to protect and defend. Instead we see them being treated like they’re animals.”