The Philippines said on Friday it was freeing a notorious killer who murdered an Italian priest 23 years ago and then claimed to have eaten parts of his brain.

Justice Secretary Raul Gonzalez said Norberto Manero was granted executive clemency by former president Fidel Ramos in 1998, setting aside a life sentence for the 1985 murder.

But Ramos left office soon thereafter and Manero's release was held back by successive governments.

"We are aware that delaying release of the prisoner is punishable under our revised penal code," Gonzalez said, adding the Catholic Church did not contest Manero's release.

The convict's lawyer, Persida Acosta, told reporters Manero would leave the national penitentiary late on Friday.

Manero, his two brothers and three other companions were convicted for the abduction and murder of Tulio Favali, a member of the Rome-based Pontifical Institute for Foreign Missions (PIME), on the southern island of Mindanao.

Manero, a member of a militia known for torturing and killing suspected communist rebels, gained notoriety for the murder when he boasted he ate parts of the priest's brain after shooting him. The gang claimed the priest was a communist sympathiser.

All the other members of the gang have been freed after serving jail time.

Favali's fellow priests said they had no objections to freeing Manero because they believed he had paid for his sins.

"The sadness remains that a priest, a just man, is dead but this must not block the road to forgiveness," Romulo Valles, Archbishop of Zamboanga on Mindanao island, said in a statement posted on the church group website.