FREMONT, Ohio (AP) — A high school student’s writing assignment about overcoming obstacles in her life led to a man pleading guilty to raping her and two sisters years ago, authorities said.

Detectives in Sandusky County began investigating after school officials from Vanguard Tech Center alerted children services and the sheriff’s office about the essay.

“She had disclosed that she had been sexually abused as a child,” said sheriff Det. Sgt. Kenneth Arp.

A county judge sentenced 43-year-old Anthony Knight to 20 years in prison Tuesday after he pleaded guilty to felony charges of rape. A message seeking comment was left with Knight’s attorney.

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The three sisters said they initially reluctant to come forward because they had not reported it in the past, but they all discussed being raped and reported different forms of abuse, Arp said. The youngest was 7 when she was first sexually abused, he said.

The siblings’ statements to detectives corroborated information authorities had gathered in other interviews, he said.

“This happened years ago,” Arp said, adding that the three sisters showed a lot of courage coming forward.

Authorities credited the school with quickly alerting them to the allegations in the essay. The school’s superintendent declined to comment because he wanted to protect the student.