Police are searching for a suspect in the Sathon pier bombing who was seen on CCTV footage kicking a package into the Chao Phraya river a day before the blast.
Guiding hand: National police chief Somyot Poompunmuang talks to foreigners in the Nana area in a bid to boost confidence among tourists after Monday's bombing.
It comes as the investigation into Monday's deadly Erawan Shrine bombing appeared to stall, with police calling in outside help and authorities ramping up a public relations campaign to head off a wave of tourist booking cancellations.
The Sathon pier suspect, wearing a blue T-shirt and jeans and holding a shoulder bag, was seen dropping a package on a walkway leading over the water before appearing to fiddle with his mobile phone for several minutes.
He then moved the package about five steps and waited for pedestrians on the bridge to pass by before kicking it into the water and walking away.
Time stamps on the CCTV footage show the incident occurred around 7.20pm on Monday, less than 30 minutes after the Erawan Shrine blast.
The explosion at the pier took place at 1.20pm on Tuesday. No one was harmed.
The suspect is believed to be aged 30-40 and around 170cm tall, according to a police source.
About three to four minutes before Tuesday's blast, another man wearing a blue tartan long-sleeve shirt, black pants and a shoulder bag was seen approaching the same spot. He appeared to take photos at the scene alone and left moments before the explosion took place.
According to the source, police believe the Sathon pier bomb was intended as a backup in case the first attack was foiled, or to create fear by showing the assailants were capable of a rapid follow-up attack.
The source said the bomb could have been sealed to resist water.
The device was stuffed with ball bearings, but police have not yet ascertained whether the explosive substance used was TNT or C4, the source said.
Another police source said the explosives used at Taksin bridge and Erawan Shrine were likely TNT because debris collected from the two bombing scenes were similar. The attack at Sathon pier, however, did not appear to be aimed at causing the loss of life, the source added.
Police said the Sathon pier suspect, who appeared to be Asian, may be a Thai national but other evidence was still under review. It was not clear why it took police five days to release the footage.
The announcement of the new suspect came as police sent a sketch of the Erawan Shrine suspect to Interpol, as their investigation nears the one-week mark apparently no closer to confirming the bomber's identity.
Interpol, which has a global membership of 190 countries, has been asked to help supply information leading to the suspect's arrest, police spokesman Prawut Thawornsiri said.
Police are still in the process of reviewing CCTV footage along the routes the suspect took to the shrine and fled from the scene, he added.
Pol Lt Gen Prawut also backed away from earlier claims the suspect was a foreigner, saying it was not possible to confirm his nationality or potential motive for the attack at this stage.
A police source in the investigation team said CCTV footage showed the suspect had hailed a taxi from Yannawa district to Hua Lamphong railway station before taking a tuk-tuk to the shrine.
The taxi driver is being sought for questioning.
A 20-baht banknote which the tuk-tuk driver received from the suspect will undergo DNA analysis, the source added.
The source said the two bombings were likely to have been committed by the same group, and both may have used either mobile phone signals, Wi-Fi or Bluetooth to detonate the explosives.
As police continue to pursue new leads, authorities have also been ramping up a public relations campaign to assure tourists of their safety, with a show of force in several key transit areas yesterday.
Pol Lt Gen Prawut led officers to inspect security in front of the EmQuatier shopping mall and travelled by BTS from Phrom Phong to Chit Lom. They also inspected a skywalk linking Chit Lom station to Siam.
National police chief Somyot Poompunmuang also led a tour of Nana to reassure foreigners of their safety.
Pol Lt Gen Prawut said most foreign tourists he had spoken to were undeterred by the recent bombings and had confidence in the security measures.
He acknowledged the areas he inspected lacked effective lighting and high-definition CCTV cameras, saying police would contact private operators to help install more cameras.
Pol Lt Gen Prawut said facial recognition technology would also be deployed in the Ratchaprasong area to help police identify criminal suspects in the future.
National Council for Peace and Order spokesman Col Winthai Suvaree said the investigation into the two bombings was making headway.
He appealed for patience while forensic analysis is completed.
The sketch of the Erawan Shrine suspect has been sent to officials at all border checkpoints, he added.
The shrine blast on Monday left 20 people dead and 130 injured, many of them foreigners.
The reward for information leading to the arrest of the bomber has soared to 10 million baht, after Panthongtae "Oak" Shinawatra, the only son of fugitive former prime minister Thaksin Shinawatra, added seven million baht to the bounty.
Two million baht will be given to those who provide a useful tip-off and five million baht to investigators, Mr Panthongtae said.
The Royal Thai Police Office had previously pledged two million baht, and a businessman has promised another one million baht.
The Justice Ministry's Rights and Liberties Protection Department and the Tourism and Sports Ministry have distributed financial support to the relatives of 15 of those killed in the bombing — 13 foreigners and two Thais, according to Col Winthai.
City Hall has given financial support to nine injured victims, he said. Fifty-six people remained in hospital last night.