But apart from a rough portrait, authorities have few solid leads – they do not know the bomber’s motive, where he is from or if he is still in Thailand.
The sketch was released after grainy security video footage showed the man leaving behind a backpack just 15 minutes before the blast at a popular shrine.
Police said the picture was also partly based on a description provided by a motorcycle taxi driver believed to have given him a ride on the night of Monday’s explosion.
Two days after the attack – which authorities have called the worst in Thai history – the open-air Erawan Shrine reopened. But little is known about who carried out the blast that left 20 people dead and more than 120 injured, and no one has claimed responsibility.
Police chief Somyot Poompanmoung said authorities do not know if the suspect seen in the video was still in the country, whether he was Thai or a foreigner and were wondering if he wore a disguise to mask his identity.
The sketch released yesterday showed a young man in glasses with bushy, dark hair that is cropped at the sides.
Mr Somyot said: “If citizens or anyone can give us information or clues that leads to the arrest of this man I have set a reward of one million baht.
He said police believe the bomber had accomplices. “He didn’t do it alone, for sure. It’s a network,” Mr Somyot added.
Police spokesman Lieutenant General Prawut Thavornsiri said security footage appears to show two possible accomplices who are also considered suspects.
On Tuesday, police released still photos of the man seen in the video, wearing a yellow T-shirt and shorts. His hair appears shaggier in the video than the police sketch. The photos show him both with and without a large, black backpack.
A video posted separately on Thai media, showed the same man sitting on a bench at the shrine, taking off the backpack and leaving it behind as he stood up to fiddle with his phone and then walked away. Time stamps on the footage show that he left the shrine 15 minutes before the explosion, just before 7pm.
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 yesterday before heading into a three-hour meeting of national police commanders.
Mr Prayuth has called the attack “the worst incident that has ever happened in Thailand” and vowed to catch the perpetrators.
The Erawan Shrine, is a revered spot among 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 tourists.