Police say closed circuit television has captured the moment an attacker threw a grenade into a crowd of anti-government protesters in central Bangkok, injuring 28 people, seven of them seriously.
The man wearing a cap and carrying a bag over his shoulder could be seen clearly in the CCTV footage released by police.
They said it would be used to back a warrant for the arrest of the man who was not immediately identified.
Two explosions about two minutes apart shook a protest site near Victory Monument in central Bangkok on Sunday afternoon, the second daylight attack using grenades in 48 hours.
Police said footage showed the man tried to throw one grenade into a tent behind a rally stage but missed and the grenade hit the roof of a coffee shop and exploded.
He threw another grenade and fired shots at protesters who started to chase him before flagging down a motor cycle taxi, police say.
The attack comes as tensions soar in the city of 12 million people after a week of almost daily shooting attacks on protest sites and small explosives hurled at the homes of protest supporters.
The footage has been released amid angry accusations over who was responsible for a blast on Friday in the middle of a protest parade that left one protester dead and 35 wounded.
Police said for that blast they were seeking two men, one believed to be aide of a former opposition Democrat party MP who were seen in a video clip of the explosion.
The Democrats support the protest movement trying to topple government of prime minister Yingluck Shinawatra, raising suspicion is was a staged attack designed to blame her supporters.
But protest and Democrat leaders angrily denied any role.
At least one of the injured in Sunday's attack was a journalist.
The escalating violence has renewed speculation that Thailand's powerful military will intervene to end the crisis that has left nine people dead and hundreds injured during two months of protests that are dragging down South-East Asia's second largest economy.
Supreme military commander Thanasak Patimaprakorn said the situation had become serious with the country like a patient suffering from cancer who needs immediate attention.
General Thanasak urged all sides to negotiate but conceded there was no mediator to broker and end to the crisis.
"I have only one wish now which is that everyone sit down and talk and that they are all safe," he said.
"This is the military's stance at this time.
The military has staged 18 coups or attempted coups since the 1930s.
Despite the violence protest leaders have vowed to continue their campaign aimed at forcing Ms Yingluck to resign and call off elections set for February 2.
"It (the attack) is an outrage. We would like you to come out and join our fight...if we don't fight, we will fall in to become Thaksin's slaves," said Akanat Promphan, spokesman for the protest movement.
Thaksin Shinawatra is Yingluck's elder brother who the protesters accuse of running the country from Dubai where he lives to avoid a jail sentence for corruption.
Yingluck denies the claim and has urged protest leaders to meet her to negotiate an end to the crisis but they have refused.
The number of protesters on Bangkok's streets has dropped significantly over the past few days, indicating the protests may be running out of steam.
- FFX Aus