Hundreds of captives who were beaten, abused and held in squalid conditions at a purported Islamic school in northern Nigeria escaped prior to a raid this week, police said on Tuesday.

Nearly 300 men and boys had been at the facility in the Daura area of Katsina, the home town of President Muhammadu Buhari, where police said they discovered “inhuman and degrading treatments” following a raid to free the remaining students.

It was the second such school in less than a month to be raided by police, after hundreds were freed from similarly degrading conditions in neighboring Kaduna state.

The 67 inmates who were freed by Katsina police were shackled in chains, and many were taken to hospital for treatment, police superintendent Isah Gambo told Reuters.

“I tell you they were in very bad condition when we met them,” Gambo said.

A freed captive told Reuters on Monday that the instructors beat, raped and even killed the men and boys held at the facility, who ranged from 7 to 40 years of age.

While the institution told parents it was an Islamic teaching center that would help straighten out unruly and wayward family members, the instructors instead brutally abused them and took away any food or money sent by relatives.

Police said they had arrested the owner of the facility and two teachers, and were tracking other suspects.

The more than 200 captives who escaped were still missing, Gambo said. Police were working to reunite the others with family members.

“The inmates are actually from different parts of the country – Kano, Taraba, Adamawa and Plateau States,” he said. “Some of them are not even Nigerians. They come from Niger, Chad and even Burkina Faso and other countries.”

Islamic schools, called Almajiris, are common in the mostly Muslim north of Nigeria. Muslim Rights Concern, a local organization, estimates about 10 million children attend them.

While Buhari said the government planned to ban the schools eventually, he has not yet commented on the Katsina school.

After the Kaduna raid, the president called on traditional authorities to work with government to expose “unwanted cultural practices that amount to the abuse of children”.