Mr Pruek said he was not aware that protesters were to be targeted by unknown gunmen who fired bullets at a convoy of the Network of Students and People for Reform of Thailand (NSPRT) on the expressway in Nonthaburi.
Sgt Wasant Khamwong, a security guard for the network, was killed and four other protesters were injured.
"If you want to kill someone, you don't tell him first. Everybody suspects me. It's not an issue and it's nonsense," he said, speaking publicily for the first time about the attack.
Mr Pruek, who claimed he was now Chiang Mai, said he only wanted to warn demonstrators to avoid taking the expressway in his ''Lungying Tawasawang'' Facebook post.
The red-shirt member is a prime suspect in the ambush because he had written on Facebook hours before the firing that demonstrators could face attacks on the expressway on their return from a rally at the government complex on Tuesday. He also said on his message that Wuthipong Kachathamkul, alias Ko Tee, was waiting for them.
It happened to be true. And he wrote again on the social media shortly after the ambush that he was not involved in it.
Mr Pruek claimed he posted it in Lamphun and dismissed his links to Mr Wuthipong, saying he mentioned the name of the red-shirt leader in Pathum Thani to add credibility to his posting.
Police have not yet found the attackers believed to have fired bullets from a building near the expressway at the convey. They hit a truck where Sgt Wasant was riding and a bus carrying other protesters.