The radical Islamic terror group National Thowheed Jamath was officially blamed Monday for the series of coordinated bombings that killed at least 290 people and wounded 500 on Easter Sunday in Sri Lanka, though authorities warned the domestic cell likely had overseas help.

“We do not believe these attacks were carried out by a group of people who were confined to this country,” said Sri Lankan Cabinet spokesman Rajitha Senaratne. “There was an international network without which these attacks could not have succeeded.”

So far, 24 suspects have been arrested in the aftermath of the attacks carried out by seven suicide bombers at vulnerable sites where people felt their safest: hotels and churches.

“It’s very difficult to identify the bodies,” Father Shelton Dias of the Archdiocese of Colombo told Al Jazeera of the victims at one church.

“They are so disfigured. With some of the children, it’s just their shoes.

“Terrorism has no mercy.”

An international approach has formed around the painstaking search for answers, with the FBI and Interpol among the global organizations aiding Sri Lankan authorities.

But there was also an inward focus, as government officials tried to figure out how the murders were pulled off when intelligence told them nearly three weeks earlier that an attack could be coming.

Senaratne revealed Monday that Sri Lankan intelligence agencies began issuing internal warnings as early as April 4 that a bombing could be in the works. Reports on Sunday had said that t was April 11.

But the word traveled slowly through some circles of the infighting-plagued Sri Lankan government — and never even made it to the desk of Prime Minister Ranil Wickremesinghe, who was barred from Security Council meetings amid an ongoing feud with President Maithripala Sirisena.

Word that the slaughter could have been stopped left many aghast.

“We placed our hands on our heads when we came to know that these deaths could have been avoided,” said Malcolm Cardinal Ranjith, archbishop of Colombo. “Why this was not prevented?”