DNA evidence, including a severed head from the remains of the two bombers, is being examined.

Investigators said that the attackers built the bombs in a room of the Marriott hotel they had checked into, two days before the attack.

Security video from the hotel shows a man with a suitcase and backpack entering the hotel restaurant shortly before an explosion.

Police have not confirmed whether the man is a suspect.

Speaking to Al Jazeera, the head of security at the Marriot said: "We had two security officers who saw this man ... carrying a big back pack on [his front].

"[When questioned] he said I'm going to see my boss... [but] couldn’t come up with the name and he just kept walking.

"He moved forward five metres and the bomb detonated."

Prime suspect

No one has yet claimed responsibility for Friday's blasts, in which devices packed with nails, ball-bearings, nuts and bolts were used.

However, suspicion has fallen on the Jemaah Islamiyah (JI) group and its allies.

Sidney Jones, of the International Crisis Group, told Al Jazeera that one of the prime suspects "has to be Noordin [Mohammed] Top", the Malaysian-born leader of a splinter JI group.

In depth


 Video: Witness to Jakarta bombing
 Video: Jakarta blast caught on tape
 Indonesia's war on Jemaah Islamiyah
 Survivors describe blast panic
 President vows to catch bombers
 Timeline: Indonesia bombings

"The police were actively looking for him just last week in a town in central Java where they found explosives similar to those used in the hotels [attacks]," she said.

"They have been close on the trail of some of these people in the past and I am sure we will see a wave of arrests in the aftermath of this bombing."

Ansyaad Mbai, Indonesia's security ministry's anti-terror desk chief, confirmed that there was evidence that Top was behind the attacks.

"There are strong indications that Noordin Top's group is behind the attacks because the bombs were hand-made and the tactic was suicide bombings," he told the AFP news agency.

They were also the same as devices discovered at an Islamic boarding school in central Java last week during a raid on Noordin's suspected hideout, Mbai said.

Noordin's Indonesian wife was reportedly arrested in the raid.

"I can't say the attacks yesterday were an act of retaliation for the recent arrests, but I can say that the police are getting very close to capturing Noordin," Mbai said.

Under scrutiny

While the hotels claim their security measures have been adequate, Indonesia's wider national security procedures are once again under scrutiny.

Jack Suwanlert, the security operations director for Marriott International, has defended screening procedures at the Marriott hotel, but the bombers were apparently able to evade the metal detectors and vehicle checks put in place to ward off attackers.

Jones said bombers learn from their mistakes.

"The fact that they are using a new method this time [some are saying the bombers swallowed explosives to avoid detection] may be a signal that they've learned that past methods were dangerous," she said.

"The bombers come from small breakaway groups. We may find that people involved in this bombing had no connection before with Jemaah Islamiyah except for some senior experienced people."

While there are believed to be more than 1,000 active JI members in Indonesia, in recent years JI has become a highly fractured organisation, according to Al Jazeera's Step Vaessen.

Foreigners killed

Four foreigners - a New Zealand businessman, two Australians and a Singaporean - were confirmed dead and at least another 18 were among the scores of people who were injured.

Australia has said that three of its citizens are missing after the blasts, including Craig Senger, a diplomat, who was in one of the hotels for a business meeting.

He is believed to have been  killed, but this has not been confirmed.

The injured include citizens of Australia, Britain, Canada, China, India, Italy, Norway, South Korea, the Netherlands and the US.

There are also reports of an Indonesian being among the dead.

The attack on the Jakarta Marriott is the second bombing of the hotel. A suicide bombing in 2003 left 12 people dead and injured more than 150.