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.
CCTV footage has emerged showing the man wearing a blue T-shirt and fiddling with a mobile telephone.
On Thursday, meanwhile, a journalist found shrapnel and ball bearings embedded in a wall near the shrine where the explosion took place, and when he brought the evidence to the police headquarters, he was told that the office was closed. Asked if the man in the video was linked to the bombing at the shrine, he said police had not yet drawn that conclusion.
“The thing he kicked in the water might just be garbage, we don’t know yet”, he said. “And our in-depth investigations reveal that foreigners of unknown nationality came to Thailand in 2011 to provide training on such a technique”, the source said.
Police are convinced the attack was planned and coordinated by a network.
Separate security footage now points to three men who are wanted for questioning over the bombings.
Security footage also shows a third man suspiciously taking photographs at the canal moments before the second bomb exploded there.
The source said the detonation of a TNT bomb could be delayed for several days if an electric circuit was involved. On a police arrest warrant he is described as a “foreign man”, although a military spokesman said a connection to worldwide terrorism seemed unlikely.
But Thai media now report officials saying foreign techniques were used in the both the shrine and Sathorn-Taksin bombs.
“Such a technique did not exist in Thailand before”.
The ongoing political struggle has seen repeated rounds of deadly street protests, including grenade and small pipe bomb attacks.
Thailand’s military government has ramped up a public relations campaign in an attempt to head off mass cancellations of tourist bookings in response to the bombings, particularly from China.
The Bangkok bombing has captivated people across the country, but attacks in southern Thailand have killed more than 6,500 since January 2004, according to Thitinan Pongsudhiral, chairman of the Center for Strategy Studies at Victoria University of Wellington, New Zealand. The shrine – a popular tourist attraction that typifies the kingdom’s unusual blend of Hindu and Buddhist traditions – and its surrounding had already been largely restored.
Senior police have also been making walkabouts in areas popular with tourists, including Bangkok’s seedy red light districts.
He failed to give any further details, but did refute previously expressed fears that Chinese citizens (four of whom died) had been the focus of the attack, claiming they were not the “direct targets”.
So soon after the attack in politically volatile Thailand, which before the coup experienced repeated outbreaks of deadly street violence in a decade-long power struggle, it is hard to gauge the long-term impact of the blast on tourism.