An altercation at an Oklahoma public school involving a 16-year-old nonbinary student who died the next day began after the student “poured water” on girls who had been making fun of the teenager, according to a body camera video interview released by the Owasso Police Department late Friday.

The video of the 16-year-old student, Nex Benedict, talking to an Owasso officer provided the fullest account yet of what took place inside the girls’ bathroom on Feb. 7. The altercation drew national scrutiny after gay and transgender rights groups focused attention on Nex’s death as an example of the dangers faced by gender-nonconforming students.

The interview, which lasted about 20 minutes and took place at a local hospital, provided new details of the confrontation at the West Campus of Owasso High School. Nex, who used they and them pronouns with peers, described how they “blacked out” while being beaten on the floor of the bathroom by three girls who had previously mocked Nex and their friends “because of the way that we dress.”

“We were laughing. And they had said something like, ‘Why do they laugh like that?’ They were talking about us in front of us. And so I went up there and I poured water on them” from a plastic water bottle, Nex told the officer. “And then all three of them came at me,” Nex said.

The department also released surveillance video from inside the school showing students, including Nex, entering the bathroom and, separately, Nex walking through the halls with a staff member after the confrontation.

And the department provided audio of the 911 calls made by Sue Benedict, Nex’s grandmother and guardian, on the day of the altercation and then on Feb. 8 as she urgently sought an ambulance for Nex.

Ms. Benedict told the dispatcher around 1 p.m. that Nex kept saying they had a headache and Ms. Benedict was unsure if it was from Nex’s head injury. Nex hit their head on the bathroom floor, Ms. Benedict said, describing the altercation the previous day.

Ms. Benedict told the dispatcher that Nex took medication at night for anxiety and “mood swings” but that Nex had not taken any that day. Asked whether Nex took illicit drugs, Ms. Benedict said no, though Nex “has vaped.”

The videos, while providing more information, did not answer the question of how Nex died. The police department has said that the death is still under investigation but that preliminary results of an autopsy found Nex “did not die as a result of trauma.” The state medical examiner’s office said its report on the autopsy and toxicology results would be made public when it was ready.

The death of a nonbinary student following an altercation at school prompted renewed scrutiny of Oklahoma’s restrictive policies for L.G.B.T.Q. students — including new laws regarding bathroom usage and barring gender-transition care for minors. The state superintendent of schools, Ryan Walters, who has been criticized for his anti-transgender rhetoric, said the death was a tragedy but did not alter his views, including on bathroom usage or discussions of gender.

Rights groups and transgender students have said the political rhetoric by Oklahoma leaders in the Republican-dominated state has been viewed by some students as permission to harass and bully their classmates.

In their interview with the officer, Nex spoke from a bed at Bailey Medical Center in Owasso, with Ms. Benedict sitting nearby.

Ms. Benedict told the officer that the girls would not leave Nex alone. “They’re making comments, they’re throwing stuff, they’re calling us names,” Ms. Benedict said, recounting what Nex had told her.

The officer then asked Nex to describe what happened. Nex said that while they had told their family about the earlier bullying, they had not reported it to school officials. “I didn’t really see the point in it,” Nex said.

Nex said that other students had focused on Nex and their friends because of their way of dressing. The topic of Nex’s gender identity or that of their friends did not come up in the interview. Ms. Benedict referred to Nex using their birth name and pronouns during the police interview and in calls with 911.

Just before the altercation, Nex had been talking with friends inside the bathroom, while the girls were talking with their own friends nearby, Nex said.

During the altercation, “they grabbed onto my hair. I grabbed onto them. I threw one of them into a paper towel dispenser, then they got my legs out from under me and got me on the ground,” Nex said. “My friends tried to jump in and help, but I’m not sure, I blacked out.”

The officer suggested to Nex and Ms. Benedict that criminal charges might not be wise to pursue because Nex was “the one who started it by throwing an object or an item onto another individual.”

That fact “does not give them the right to put their hands on you,” the officer said. “It’s just, I hate to see you both, criminally wise, get hung up on something so minuscule. But I am here to do that if that’s what you like.” Ms. Benedict and Nex ultimately agreed not to pursue charges at that time.