National Thowfeek Jamaath (NTJ) was named by Sri Lankan officials as behind the bombings, which left 321 people dead and 500-plus others injured.
The Islamic group was headed by Zahran Hashim, who was also known as Mohammed Zahran. According to Muslim leaders in Sri Lanka, he became known to them about three years ago.
"It was basically a hate campaign against all non-Muslims," said Hilmy Ahamed, vice president of the Muslim Council of Sri Lanka. "Basically, he was saying non-Muslims have to be eliminated."

Ahamed and N.M. Ameen, president of the council, claimed to have alerted authorities to Hasmhi but said they took no action.
Anne Speckhard, the director of the International Center for the Study of Violent Extremism, said that she was at a conference in February when a Sri Lankan intelligence official approached her and described a violent, homegrown jihadi group that "would just disappear" when the government tried to crack down on them.
"The intel person kind of came up to me and said, 'You know, we're kind of worried about this new group and there's some activity going. What do you think?'" Speckhard said. "It just kind of blows my mind that's who it was."

While NTJ was blamed for the attack, Sri Lankan officials said it was a "small organization" that had "an international network" for support. Investigators said the bombings were apparently in retaliation for the March 15 shootings of 50 people at two mosques in New Zealand.
ISIS, also known as the Islamic State, claimed responsibility for the Sri Lankan bombings on April 23 through its Amaq propaganda agency.

According to a police report from 2016, Hasim and his followers held a meeting outside another mosque, bringing swords and clubs that they used in a clash with people in the area. Police wanted to apprehend him but he fled the area and was believed to have left the country, possibly relocating to the Maldives.
No one knew where he was until he showed back up to set off one of the bombs, according to the outlet.

"What we have seen from the CCTV footage is that all the suicide bombers were carrying very heavy backpacks. These appear to be crude devices made locally," a source said.
From the information that appeared in the report, it appeared that the brother who bombed the Shangri-La was Setiawan, as other information stated by police in court said that his wife set off a bomb when police arrived at their home following the bombings.
The couple's two children were killed in the blast.