BANGKOK — (CNN) The man suspected of carrying out the deadly bombing of a popular shrine in the heart of the Thai capital likely had accomplices, Thai police said.

Examination of surveillance video footage from the Erawan Shrine indicates at least two other people were helping the main suspect in the attack that killed 20 people and wounded more than 120 on Monday evening, police officials told a news conference Wednesday.

Authorities are hunting for the man seen on a surveillance video putting a backpack under a bench in the shrine and then walking away shortly before the blast went off.

Beyond the yellow T-shirt and dark-framed glasses he was wearing, little is known so far about the man who police say they are “very sure” is the bomber.

Here’s where things stand with the investigation into the attack, which authorities have described as a deliberate act of terror:

The suspect

Police say they don’t yet know the suspect’s identity or whether he is Thai or a foreigner.

They are studying more than 10 days’ worth of CCTV footage from the scene to try to find out more.

The surveillance footage from Monday evening shows the suspect in the yellow shirt sitting down on a bench in the shrine at 6:52 p.m. and hiding the backpack under the bench, according to police spokesman Lt. Gen. Prawut Thavornsiri . The man left the scene without the backpack and the blast went off minutes after he set it down.

Police also noted that the suspect had material wrapped around both of his forearms, which they say could indicate he had previously sustained some kind of injury.

Investigators have questioned the motorcycle taxi driver the suspect used after the explosion, Prawut said Wednesday without providing details on what he told them.

A reward of one million Thai Baht ($28,000) is being offered for information leading to the suspect’s arrest, he said.

The device

The blast at the shrine was caused by a pipe bomb containing wheel bearings, according to police.

Investigators believe the explosive device was assembled in Thailand because many of its parts, including the pipe, were made in the country, Prawut said.

CNN security and intelligence analyst Bob Baer said it was unusual for a pipe bomb to kill so many people and cause so much damage.

“It would be a very sophisticated pipe bomb,” he said.

Another blast that struck near a river pier in Bangkok on Tuesday was caused by a similar device, Prawut said. That explosion went off in the water and didn’t hurt anyone, but it was still “quite big,” he said.

Royal Thai Police Commissioner Gen. Somyot Poompanmoung said Wednesday that investigators were so far unable to establish a link between the two explosions, adding that they have no leads on who might be behind the Tuesday blast.

The motive

There has been no claim of responsibility for the bombing, and comments from Thai officials have so far been vague.

“From this incident, it is apparent that there are active individuals or groups that harbor the intention to damage Thailand, who may be pursuing political gain or other intentions by damaging the economy and tourism,” Prime Minister Prayuth Chan-ocha said Tuesday.

Analysts have speculated about a wide range of groups — including opponents of military rule in the country or a rogue faction in the army or police — but there is so far no evidence to link the attack with any of them.

Asked Tuesday if there was any information on a possible motive for the attack, police spokesman Prawut said it was too soon to reach any conclusions.

The victims

Thai authorities still haven’t identified all of those killed in the bombing, many of whom were from other countries.

The shrine is a popular tourist site and sits at a busy intersection near a big shopping mall.

China’s state-run news agency reported that six Chinese citizens, two of them from the special administrative region of Hong Kong, were killed. Malaysia’s national news agency Bernama said that four Malaysian citizens, all from the same family, were among the dead.

Officials have said that five Thais, a Briton and a Singaporean also died in the blast.

Police had put the overall death toll at 22, but on Wednesday they revised it down to 20, saying the confusion had arisen from the sheer number of body parts scattered at the scene.

Motorbike taxi driver Theerasak Kultham, 20, was among the many people wounded. He told CNN he was stopped at a red light while taking a customer to a mall when he heard a loud explosion.

He saw his customer’s arm was covered in blood and realized his own back was numb and bleeding. Doctors said he had two shrapnel injuries — and one piece may have to work its own way out.

“I’ve never been through (anything) like this before. I’m still scared,” he said.

The shrine

Monks in orange robes on Wednesday chanted and prayed for departed souls at the shrine, which bore the scars of the powerful blast that tore through the crowd of visitors on Monday evening.

A golden statue of the four-headed Hindu god Brahma was missing most of one of its jaws. Fresh cement had been poured over the crater caused by the explosion.

Tributes of flowers were piled on a table and pinned to the railings outside the shrine. “Rest in peace,” read one paper sign attached to a barrier.

Some people prayed, others took photos.

The site is popular among Buddhists as well as Hindu and Sikh members of Thailand’s Indian community.

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