The two men who were suspected to have been involved in Monday’s blast after they were both seen via security cameras standing near the prime suspect, wearing a yellow shirt at the scene at Erawan Shrine, which claimed the lives of 22 people and heavily wounded more than 123 people, according to Thai national spokesman.
The footage led the police to suspect the pair, one in a red shirt and the other in a white shirt, may have been the attacker's accomplices.
A police spokesman stated that they were now convinced that the two men - a Chinese tourist and his Thai guide - were not involved.
The Thai guide told the police that he had taken the Chinese tourist to the Erawan shrine on behalf of a mutual friend, according to police spokesman Prawut Thavornsiri.
Adding that the Chinese national returned home a day after the bomb, Mr Thavornsiri said, stressing that neither men were "likely involved."
Col Winthai Suvaree, a spokesman for the ruling military junta, said earlier on Thursday that the preliminary conclusion was that it was "unlikely" the blast was caused by the work of an international “terror” group.
However, Suvaree later told Associated Press that "we still have to investigate in more detail."
Images of the main suspect show him getting out of a tuk-tuk 18 minutes prior to the blast carrying a black backpack.
The suspect was then seen walking into the shrine, taking off the backpack, and placing it beneath a bench on the ground.
"The man was seen on security camera sitting on a bench in the compound of the shrine after leaving his bag behind the bench," Closed-Circuit Television (CCTV) reported.
He then walks out within less than three minutes before the explosion happened.
The cameras then pick him up on the back of a motorbike taxi, heading south, towards Lumpini Park, where the driver has told police he dropped him off.
Police authorities said that they have lost all traces of him since then.
The tuk-tuk taxi driver who transported the main suspect to the shrine, is also being questioned by the police, but the authorities are still not able to identify the name and nationality of the suspect.
According to General Prayut, it is believed that the main suspect is a member of an “anti-government group based in Thailand’s north-east” referring to the Red Shirt movement.
The Red Shirt movement who represent the poor districts of the country’s northeastern part support ousted Prime Minister Thaksin Shinawatra and her sister.
The latest coup in Thailand overturned the elected president Yanigluck Shinawatra and his cabinet in 2014.
The movement has been blamed for instigating political unrest in the country, carrying out grenade attacks throughout the nation however it had never attempted an attack as massive as Monday’s one.
Following the Prayut’s statement Maj Gen Weerachon Sukhonthapatipak said that government officials have not confirmed the identity of the suspects adding that no group has yet claimed responsibility for the attack, explaining that no information can be retrieved except from the footage circulating TV channels and social media.
Professor Panitan Wattanayagorn, a national security specialist and advisor to defence minister and deputy premier General Prawit Wongsuwan said that “We are not ruling out any suspect groups,’’
“The list of suspects is small. They are looking for just a few people. And police chief General Somyot Poompanmoung believes they are still in Bangkok,’’ he told The Straits Times.
According to the rumors from some media outlets, General Prayut ordered an investigation against ousted premier Thaksin Shinawatra for having part in the deadly blast.
The country has also been struggling with a decade-long insurgency in its Muslim majority located in the southern provinces. The conflict between rebel groups and the government troops have claimed 6,400 lives so far.
Government spokesperson, Sukhondhapatipak discarred the speculations concerning the involvement of the southern insurgency in the attack saying that the style of the attack in which three kilograms of explosives were used to prepare the two pipe bombs that hit the capital of the country did not match the tactics of Muslim insurgents from the country’s south.
He also pointed that the Muslim insurgency had never planned such a major attack outside the southern Thailand, till now.
Army Chief General Udomdej also backed the statement of the Major General Sukhondhapatipak saying on television that the bomb blast at Erawan “ does not match with incidents in southern Thailand”.
The main suspect remains at large, but authorities told BBC that they believe he has not yet left Thailand.
Police authority had stated that at least 10 people were suspected of involvement in the blast, emphasising that their prime target was foreign.
National police chief Somyot Pumpanmuang said that he believed the attack was planned at least a month in advance.
Prime Minister Prayuth Chan-ocha has called the explosion to be the "worst ever attack" on Thailand.
Twelve people of the 22, whose lives were claimed by the blast, were foreigners - including nationals from China, Hong Kong, the UK, Indonesia, Malaysia and Singapore.
On Tuesday, China expressed its strong condemnation for the attack and urged the Thai government for a full investigation to find out who was behind the deadly blast, according to a statement which was posted from Chinese Foreign Ministry spokeswoman Hua Chunying’s website.