The man, Dahiru Adamu, 25, was crouching on the floor in the sprawling police headquarters here, summoned to give an accounting of the terrible night of March 7, when, he said, he and dozens of other herdsmen descended on a slumbering village just south of here and slaughtered hundreds with machetes, knives and cutlasses in a brutal act of sectarian retribution.

On Monday and Tuesday, 332 bodies were buried in a mass grave in the village of Dogo Na Hawa, the Nigerian Red Cross said Wednesday. Human rights groups and the state government say that as many as 500 people may have been killed in the early hours of Sunday morning, in three different villages.

Sunday’s killings were an especially vicious expression of long-running hostilities between Christians and Muslims in this divided nation. Jos and the region around it are on the fault line where the volatile and poor Muslim north and the Christian south meet. In the past decade, some 3,000 people have been killed in interethnic, interreligious violence in this fraught zone. The pattern is familiar and was seen as recently as January: uneasy coexistence suddenly explodes into killing, amplified for days by retaliation.

Mr. Adamu, a Muslim herder, said he went to Dogo Na Hawa, a village of Christians living in mud-brick houses on dirt streets, to avenge the killings of Muslims and their cattle in January.

The operation had been planned at least several days before by a local group called Thank Allah, said one of Mr. Adamu’s fellow detainees, Ibrahim Harouna, who was shackled on the floor next to him. The men spoke in Hausa through an interpreter.

“They killed a lot of our Fulanis in January,” Mr. Adamu said, referring to his ethnic group. “So I knew that this time, we would take revenge.”

His victims were sleeping when he arrived, he said, and he set their house on fire. Sure enough, they ran out.

“I killed three people,” Mr. Adamu said calmly.

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