BANGKOK — Thai authorities Tuesday said they were pursuing a man captured on video before the bombing of a religious shrine in Bangkok the previous night, an attack that killed at least 20 people, many of them tourists.
Security footage showed the man at the Erawan Shrine taking off his backpack and leaving it under a bench. The footage and other images, which were widely shared on social media, showed the man wearing a bright yellow shirt.
"It is quite clear that he is the perpetrator in this case," said Lt. Gen. Prawut Thavornsiri, a spokesman for the Thai national police.
Police described the man as a potential suspect based on analysis of more than a dozen security cameras in the area.
Prayut Chao-ocha, the head of Thailand's military junta, said the blast could have been perpetrated by groups based inside or outside the country.
"There are individuals or a group of people in our country who have ill will to the country," he said. "This is a movement that probably wishes for political gain, and to destroy the economy, destroy tourism, among other things."
Prawut said the bomb detonated several minutes after the suspect departed on a motorcycle taxi. Investigators believe that materials for the bomb had been bought and assembled in Thailand, he added.
"The bomber was a professional," Prawut said.
Among the dead were five Thais, two Malaysians, two mainland Chinese, two Hong Kong Chinese and a Singaporean. Police said that arriving at a precise death toll was difficult because bodies had been dismembered by the blast.
With the city already on edge after the attack Monday, video circulated on social media Tuesday of another explosion, under a Bangkok bridge. No injuries were reported.
The search for a perpetrator in the attack has partly been tainted by the country's poisonous political divides. After a decade of political turmoil that has turned Thailand's public institutions into factions warring for supremacy.
Hours after the blast Monday evening, which also left more than 100 people wounded, senior officials of the military junta that seized power last year ruled out any connection to the continuing Muslim insurgency in southern Thailand. The head of the Thai army, Gen. Udomdej Sitabutr, said the type of bombing and the way it was carried out made any link to that conflict unlikely.