The government insists the Central Festival Samui bombing was motivated by anti-coup political sentiment though the attackers might also be involved with insurgent groups in the far South.
Deputy government spokesman Maj Gen Sansern Kaewkamnerd said the evidence so far pointed to a group of people behind violent incidents in Bangkok, including the explosions near Siam Paragon on Feb 1 and a grenade attack at the Criminal Court's car park on March 7.
While some of the attackers are thought to be linked to insurgent groups, with the possibility they were hired by those behind the plot, the main motivation is thought to be anti-coup sentiment.
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Maj Gen Sansern said the group used a stolen pickup truck from Yala for the bomb attack to throw authorities off the trail. "There are attempts to connect the [Samui] explosion to the southern insurgency in the deep South. The group responsible for the blast is trying to mislead the investigation. But authorities have solid evidence, so the insurgency link is quite weak," he said.
Following the incident, soldiers detained Narin Umnongbua in Nonthaburi, a red-shirt supporter, for questioning. He allegedly posted a Facebook message about 10 hours before the explosion on Koh Samui warning that a massive attack was being planned for Surat Thani.
The explosion took place at 10.30pm on Friday in the basement car park of Central Festival Samui and injured seven people, including a 12-year-old Italian tourist, and damaged about 10 vehicles. About the same time, a fire broke out at the Surat Thani Cooperative in Punpin district, destroying a food court. At least three people are being detained for questioning for suspected involvement in the explosion.
Army Commander Gen Udomdej Sitabutr said authorities are focussing on two theories: a personal conflict between the shopping mall and its former employees, and political violence.
He said he did not believe the Samui blast was the work of militants widening their attacks to other areas.
According to a security source, Central Festival Samui had earlier fired a group of security guards. These ex-workers are natives of the deep South and could have hired militants to plant the bomb.
National police chief Somyot Pumpanmuang, however, insisted Sunday that no possible motives, including southern insurgents expanding their campaign of violence, have been ruled out. He said police are working on three possible motives and the two others involve a political conflict and a personal conflict.
Pol Gen Somyot said Mr Narin remains in military custody and will be handed over to police if he is linked to the Samui bombing.
Pheu Thai member and red-shirt leader Worachai Hema called on authorities to thoroughly investigate the attack rather than relying on a Facebook post.
"If he is involved, there must be evidence connecting him to the incident. He could be simply seeking publicity," he said. According to a military source, Mr Narin denied having posted the message but someone else used the user name "M Suadaeng" to post it.
Meanwhile, Fourth Army commander Prakan Chonlayuth said investigators believe some of those linked to the Samui bombing come from the deep South and some are staying on the island.
But it is too early to conclude if the blast is linked to the insurgency.
Songkran revellers fire water guns at beauty queens on a float which paraded through downtown Koh Samui to celebrate the Songkran festival yesterday. The parade went on amid tight security in the wake of the Central Festival mall bombing. THANARAK KHUNTON
Meanwhile, a source close to the investigation said there are at least two people involved in the bombing and police have camera footage of the pickup truck used in the blast being taken aboard a ferry from Don Sak to Samui.
The pickup truck was reported stolen from Abdulrosa Dumeedae, a 52-year-old driver with the La-ae tambon administrative organisation in Yaha district of Yala, about 8am on March 31.
A probe found the vehicle used a main route as it left Yala and switched to village roads to avoid security checkpoints. It headed to Surat Thani via Songkhla's Saba Yoi district and the Songkhla-Nakhon Si Thammarat road, managing to avoid checkpoints. The pickup truck arrived at Don Sak pier two days before the blast.
The source said authorities are tracking the truck's route after it arrived on the island. If the bomb was assembled on the island, there would be clues for investigators to follow.
A security guard inspects tourists’ belongings at a police check-point at Samui airport, Surat Thani, following a bomb blast at the island’s Central Festival mall on Friday night. Songkran celebrations outside the shopping centre are getting underway despite the car blast that injured seven people. THANARAK KHUNTON
Evidence suggests the Samui bombers are linked to three insurgent groups in the South: one in Yala's Yaha district led by Ubaideela Romlee, one in Pattani's Nong Chik district led by Poseng Jehma, and the other in Songkhla's Saba Yoi led by Seree Waemamah, the source said.
These groups are allegedly linked to three major attacks: a bomb attack at Hat Yai airport in 2005, a bombing at the Lee Gardens Plaza Hotel in 2012, and a car bomb outside a hotel in Yala's Betong district last year.
However, the source said the group led by Mr Seree was hired by oil smugglers to carry out a bomb attack in Songkhla's Sadao district in 2013. As a result, it is also possible they were hired by some party to attack Koh Samui with the purpose unrelated to southern violence.
Meanwhile, in Narathiwat's Sukhirin district Sunday evening, insurgents opened fire on a house before setting fire to it, killing at least four people.
