OKLAHOMA CITY (AP) — Federal officials are opening an investigation into the Oklahoma school district where a nonbinary 16-year-old high school student was in a fight before dying last month, according to a letter sent by the U.S. Department of Education on Friday.

Nex Benedict, whose family says the teen was bullied at Owasso High School, died a day after the fight inside a girl’s bathroom at the school. According to family, Benedict identified as nonbinary and used they/them pronouns.

The letter revealing the investigation was addressed to the Human Rights Campaign, which had asked the the department to look into Owasso Public Schools and “its failure to respond appropriately to sex-based harassment that may have contributed to the tragic death.”

Police in the Tulsa suburb have not released a cause of death but have previously said that Benedict did not die as a result of injuries from the fight, which happened on Feb. 8.

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The department’s Office For Civil Rights stated it would investigate whether the district “failed to appropriately respond to alleged harassment,” according to the letter, which makes no reference to Benedict.

Owasso Public Schools confirmed in a statement that the district received notice of the investigation and called the allegations unsupported and without merit.

“The district is committed to cooperating with federal officials,” the statement said.

Neither police nor school officials have said what led to the fight. But Benedict’s family has said there had been harassment because of the teen’s nonbinary identity.

“We appreciate the Department of Education responding to our complaint and opening an investigation — we need them to act urgently so there can be justice for Nex, and so that all students at Owasso High School and every school in Oklahoma can be safe from bullying, harassment, and discrimination,” Human Rights Campaign President Kelley Robinson said in a statement.

Benedict walked out of the bathroom after the Feb. 7 fight but was taken to a hospital by their family and sent home that night. Paramedics were dispatched to the home the following day for a medical emergency and took Benedict to a hospital emergency room, where they later died, police said.

Benedict’s mother, Sue Benedict, has said the teen suffered bruises all over their face and eyes in the fight involving a transgender student and three older girls.

The school district has said the students were in the restroom for less than two minutes before the fight was broken up by other students and a staff member.