Six of the 1,844 prisoners who escaped from Owerri Custody Center, Imo State, returned voluntarily, according to a spokesman for the Nigerian Correctional Service.
Another 35 people chose not to flee during the attack, officials said.
The Nigeria Police Force blamed the illegal separatist group, the Biafra Indigenous People (IPOB) and its paramilitary wing, the Eastern Security Network (ESN), for the attack.
“The attackers’ attempt to gain access to the Police arsenal at Headquarters was fully and appropriately resisted by the Nigeria Police Force,” the force said in a statement on Monday, adding that no lives were lost in the incident.
Buhari also instructed the country’s law enforcement agencies to arrest fugitive prisoners and arrest perpetrators who “are believed to be deadly criminals,” said the president.
Nnamdi Kanu, leader of the separatist group IPOB, denied the organization’s involvement in the attacks.
He told CNN: “We have no part in what happened in Owerri, Imo state. That said, we recognize and acknowledge the anger, resentment and sense of injustice felt by many people – especially young people,” he said.
“So what is happening now is people trying to avenge the death of their loved ones at the hands of the Nigerian security services. Some people, I believe, have taken on the responsibility of saying ‘enough. Wherever a government allows injustice to infect , they are just inviting anarchy, Kanu added.
The Buhari regime continued to crack down on IPOB activities, fearing that an escalation of secessionism – particularly in the group’s strongholds in eastern Nigeria, could engender another Nigeria-Biafra civil war.
This led to a bitter civil war from 1967 to 1970 and more than a million people died of starvation after the war.