ABUJA, Nigeria (AP) — The suspected gunmen who killed dozens of worshippers during a church service in southwestern Nigeria in June have been arrested, Nigeria's top military officer said on Tuesday, two months after the attack which shocked many in the West African nation.

“We have arrested those behind the dastardly act in Owo,” General Leo Irabor, Nigeria's Chief of Defense Staff, said in a meeting with local media, according to the Abuja-based Daily Trust newspapers.

Neither Irabor nor the police who confirmed the arrest to The Associated Press provided further details into the development. The Nigerian general however said investigations are still ongoing and “in due course, the world will see them and others who are behind other daring attacks in the country.”

The gunmen stormed the St. Francis Catholic Church in Ondo state just as the worshippers gathered on Pentecost Sunday and killed at least 40 of them, authorities said. The incident shocked many in Ondo which is one of Nigeria’s most peaceful states and had been largely spared the violent attacks across the West African nation, particularly in the troubled north where Islamic extremist rebels of Boko Haram and other armed groups operate.

The church attack in Owo had “the imprints” of the Islamic State of West African Province, an offshoot of Boko Haram, Nigerian officials said after the attack. Security analysts have since last year warned that the Islamic rebels in Nigeria's north are now spreading to other parts of the country.

Bishop Jude Arogundade of the Ondo Catholic Diocese told AP that residents in Ondo and the church in Nigeria are already “getting frustrated that after two months, people came to kill 40 people and we do not have any information about it.”

He said the Catholic church has not been informed yet of the arrests and continues to wait to hear “the motive because we are a peaceful organization, we don’t get into politics or into controversial issues.”