National police chief Somyot Pumpanmuang has revealed that several well-known southern politicians are suspected of involvement in the Central Festival Samui bombing on Friday, which injured seven people.
Evidence has come to light of politicians providing support to those who planted the bomb, Pol Gen Somyot said.
It is the first time the national police chief has given weight to the theory that the attack was politically motivated.
For some, Pol Gen Somyot's comment puts an end to speculation of conflict between the military and police over the investigation into the attack. Although the politicians come from the South, the insurgency is thought not to be the dominant factor.
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Just hours after the blast occurred, deputy government spokesman Sansern Kaewkamnerd and army spokesman Winthai Suvaree said the blast was politically motivated and linked to previous bombings in Bangkok. They downplayed early reports of a link to southern militants.
Maj Gen Sansern said the Samui blast was either the work of an old political power network, or anti-coup elements with links to the Bangkok bombings.
Police later came out to complain that the military and government were putting unfair pressure on their investigation.
However, Pol Gen Somyot said police are not ruling out any possible motive at this stage, adding that investigators have made considerable progress in gathering evidence.
Authorities are working on three main theories. One is that southern insurgents are expanding their campaign of violence to other areas after evidence suggested the Samui bombers were linked to insurgent groups in the South.
The pickup truck used in the attack was stolen from Yala.
The other two theories are personal conflicts between the shopping mall and former employees, and political violence.
Pol Gen Somyot declined to give further details about the alleged connection between southern politicians and the explosion.
The blast took place at 10.30pm on Friday in the basement car park of Central Festival Samui.
The seven people injured include a 12-year-old Italian tourist.
About 10 vehicles were damaged by the explosion.
At the same time as the blast, a fire broke out at the Surat Thani Cooperative in Punpin district, destroying a food court.
Pol Gen Somyot denied police claimed the attack was politically motivated to help the government prolong the exercise of unlimited powers under Section 44 of the interim constitution.
Police investigations are based on evidence, he said, and police did not fabricate any evidence.
"Evidence was discovered, not fabricated. We have to discuss politics because evidence points to several well-known politicians in the South. But I insist that we are not ruling out any possible motive," Pol Gen Somyot said.
Speaking Wednesday after a meeting to follow up on the progress of the investigation, deputy national police chief Chakthip Chaijinda said it was likely some political elements were complicit in the Samui blast by providing support to the attackers.
Pol Gen Chakthip said a group of southern politicians gathered in Surat Thani about one week before the blast, which he found suspicious.
He said the Samui bombers could be linked to insurgent groups in the three southern border provinces of Yala, Pattani and Narathiwat, given that the pickup truck used in the attack was stolen from Yala.
Pol Gen Chakthip said police believed between 3-6 people were involved in the Samui blast, using two vehicles in the attack.
He said a review of footage from surveillance cameras on the mainland showed another pickup truck accompanying the stolen pickup truck from Yala.
The pickup travelled with the stolen vehicle from Yala's Yaha district, through Songkhla and Nakhon Si Thammarat until they reached Surat Thani, Pol Gen Chakthip said.
It is possible the second pickup truck was scouting the route for security checkpoints, he said.
Police believe both vehicles must have come from the deep South, he added.
Previously, a police source said the second pickup truck was not captured on security cameras at the pier in Surat Thani's Don Sak district where the stolen vehicle boarded the ferry last Friday morning.
It could have been waiting around to collect the bomber, the source said.
The pickup truck used to carry out the bomb attack was reported stolen from Abdulrosa Dumeedae, a 52-year-old official with the La-ae tambon administrative organisation in Yala's Yaha district, about 8am on March 31.
Pol Gen Chakthip said police have made progress with their investigation.
More than 20 security guards on duty on Friday night have been questioned, he said.
Another seven security guards are also being held by the military for questioning to determine whether the Friday blast could be linked to the southern insurgency.
Three guards from the deep South were on duty on the night of the explosion, police said.
Col Banphot Poolpian, a spokesman of the Internal Security Operations Command, said the latest information from security authorities suggested that southern insurgents expanding their campaign was not the key motive for the Samui car bombing.
He also said there was no connection between the bombing and the fire at the Surat Thani cooperative.
