A police manhunt was underway Wednesday for an "unidentified foreign man" shown in a security video leaving a backpack at a popular Bangkok shrine just minutes before a bomb exploded there.
Two other people seen on the video near the man are also considered suspects in Monday's deadly bombing, police said.
Authorities released a sketch of the man who left behind the backpack and offered a 1 million baht ($28,000) reward for information leading to his arrest. But apart from the rough portrait, they had few solid leads in Monday's bombing at the Erawan Shrine that killed 20 people and wounded 120 others.
The grainy security video shows the man, wearing a yellow T-shirt and shorts, sitting down on a bench at the shrine, taking off a black backpack and leaving it behind as he stands up and walks away. Time stamps show he left the shrine 15 minutes before the explosion, which struck just before 7 p.m.
The two possible accomplices are seen standing in front of the man, said police spokesman Lt. Gen. Prawut Thavornsiri. One of the men was wearing a red shirt and the other was in white, and they were seen leaving the area shortly before the man in yellow also leaves.
At a news conference, Prawut expressed uncertainty about the man's origin, saying the suspect "looks like a foreigner" but "might have been in a disguise and wearing a fake nose" to conceal his identity.
Prawut told reporters Wednesday night that police would continue to scrutinize closed-circuit TV footage of the area from before the blast for clues about suspects. He said that if the men in red and white shirts were innocent and aware of the suspicions against them, they should report to police.
Two days after the attack, which authorities have called the worst in Thai history, the shrine reopened to the public. No one has claimed responsibility for the blast at one of the capital's busiest intersections during evening rush hour.
"If citizens or anyone can give us information or clues that lead to the arrest of this man, I have set a reward of 1 million baht," National Police Chief Somyot Poompanmoung said.
"He didn't do it alone, for sure. It's a network," he said.
Police composed the sketch based on the video and a description provided by a motorcycle taxi driver believed to have given him a ride on Monday night.
The sketch shows a young man in eyeglasses with bushy, dark hair that is cropped at the sides. The warrant describes him as tall, with a pointed nose and thick lips. He faces six charges including conspiring to commit premeditated murder and conspiring to commit a bombing that resulted in death and severe injuries.
The attack has raised concerns about safety in a city that draws millions of tourists.
Prime Minister Prayuth Chan-ocha "is worried about the security of people and tourists in Thailand," the police chief said.
Prayuth has called the attack "the worst incident that has ever happened in Thailand" and vowed to track down those responsible.
On Wednesday night, police spokesman Prawut led dozens of officers on a confidence-boosting inspection of Bangkok's Soi Cowboy nightlife area, popular with foreign visitors. He told reporters there that he was "completely" confident that police can ensure security in Thai capital.
The Erawan Shrine is a revered site for Thais and tourists that transcends religion. It is dedicated to the Hindu god Brahma, but is extremely popular among Thailand's Buddhists as well as Chinese visitors.
Although Thailand is predominantly Buddhist, Hinduism has an influence on its religious practices and language. The shrine's location adds to its popularity, offering an open-air place for prayer amid the capital's gleaming shopping malls and five-star hotels.
On Wednesday, people knelt in prayer, lit incense and placed flowers at the site of the bombing. Buddhist monks in saffron robes joined the public to chant prayers.
Among those who paid respects was office worker Nuansupha Sarunsikarin, who expressed shock and sadness over the attack.
"I'm depressed for those innocent people who had to pay for something they're not involved with and now have no chance to live their lives," Nuansupha said.
Thai authorities identified six victims as Thai and four as Malaysians, along with four Chinese, two people from Hong Kong including a British citizen, one Indonesian and one Singaporean. Two victims remain unidentified.
A funeral was held Wednesday for 45-year-old Waraporn Changtam, one of the victims of the bombing. Her grieving older sister, Sawaros Kumrit, had a message for those responsible for the blast.
"I don't know who you are mad at, but don't take it out on my family," she said, adding that those killed by the bomb "were good people. They were innocent."
Bangkok was rattled by another blast Tuesday at the popular Sathorn Pier, used by river ferries. The pipe bomb exploded in the Chao Phraya River but caused no injuries. Prawut said that bombing could be related to the shrine attack.
Thailand has seen many violent attacks in recent years, particularly in a long-running insurgency by Muslim separatists that has killed over 5,000 in the country's south. Those attacks have never reached the capital, however.
Bangkok has seen politically charged violence in the past decade. The deadliest, in 2010, killed more than 90 people in two months and was centered on the same intersection where Monday's bomb went off. But none of those attacks included a bomb that seemed intended to produce mass casualties.