MANILA - (2ND UPDATE) Four individuals tagged in twin blasts at the Jolo cathedral on Sunday are already under police custody Wednesday, authorities said.

The first two—an 18-year-old student and a teacher— surrendered to the Philippine National Police Criminal Investigation and Detection Group around 10 a.m.

The student said he was the man wearing a blue-green jacket on the CCTV footage while the teacher claimed that he was the one wearing a maroon cap with a backpack in the footage.

The two said that they are not familiar with the identities of the suspects and they reported to cops to clear their names, fearing that authorities will hunt them down.

The student was the man military officials suspected as a brother of bandit leader Surakah Ingog.

Col. Gerry Besana, spokesperson of the military's Western Mindanao Command, had said Tuesday that the man, at the time wearing a blue-green jacket, was seen tinkering with a cellphone that could have been used to detonate bombs at the Jolo cathedral.

In the video, he and another man walking beside him were among those seen running away after the explosion.

Police said the 18-year-old admitted that it was him on the video but claimed he had nothing to do with the blast. He told police he was a Sulu resident and was just out to go to the market.

Meanwhile, the two other persons of interest in the double bomb attack surrendered to the Sulu Police Provincial Office around 3 p.m. Wednesday.

The two—a 17-year-old man and a 24-year-old man—are both residents of Jolo.

The two claimed that they went to a pharmacy to buy medicine and fled when they heard the explosion.

Police said they have taken the surrenderees' statements and will keep them in custody.

• READ: CAUGHT ON CCTV: Abu leader's brother may have triggered Jolo church bombs

Authorities earlier tagged the bandit Abu Sayyaf Group in the twin blasts that left 21 dead and at least 100 hurt.

-- with a report from Maan Macapagal, ABS-CBN News