JAKARTA - Sunakim, alias Afif, the most recognisable of the four militants who mounted the attack in downtown Jakarta last Thursday (Jan 14), was gunned down by an off-duty police officer just as he was about to detonate a bomb he was carrying in a backpack.

Lieutenant-Colonel Untung Sangaji told reporters during a press conference on Monday (Jan 18) at the Indonesian National Police Headquarters that he fired at the militant at close range, emptying his three ammunition magazines in the process.

He did this after he saw Sunakim putting his hand on what appeared to be a switch, and feared that he was about to blow himself up before firing.

Lt-Col Untung, who is an instructor at the Maritime Police Training Centre, was in the Starbucks cafe along Jalan M. H. Thamrin having coffee with a colleague just minutes before the attack. They had left to smoke at another coffeeshop nearby, because smoking was not allowed at Starbucks.

After hearing explosions, he rushed out of the coffeeshop only to see the police post at the nearby traffic junction in smoke.

"When I got to the police post, I heard someone from inside shouting: 'Help, help, a police officer is injured."

He added that a crowd had already gathered at the scene - not to help but to take photos with their cellphones. "Seconds later there was a sound, 'bang-bang', and one of the people who was taking a selfie fell over. I saw his feet shaking."

The photos and closed-circuit television footage of Sunakim - who was wearing a baseball cap, T-shirt and jeans - shooting into the crowd and gunning down policemen on Jalan Thamrin are among the defining images of the attack that have stunned Indonesians.

He and his three accomplices died during the siege on the Starbucks cafe and police post, less than a hundred metres from the popular Sarinah Mall.

Police previously said Sunakim, 34. was one of two militants in the group who had served time in jail for terror-related offences

Sunakim had also taken part in training at a paramilitary camp in Aceh province. The camp, set up by Jemaah Islamiah (JI) founder Abu Bakar Bashir, was shut down after it was raided by police.

The other three militants killed during the attack are Dian Joni Kurniadi, 25; Ahmad Muhazin, 25; and Muhammad Ali, 39.