He is said to be a close aide of a village headman on Koh Tao whose younger brother was taken for questioning yesterday (September 23). Police did not divulge his name.
A police source said investigators found the close aide of Woraphan Tuwichian, 49, who is a village headman and the owner of the AC Bar, is likely to know something about the murders of the two British tourists, Hannah Witheridge, 23, and David Miller, 24.
The wanted man has fled the island and gone into hiding in Bangkok, Pol Lt Gen Panya Mamen, commissioner of Provincial Police Region 8, said yesterday.
The Metropolitan Police Bureau is trying to locate him.
"We want to question him so we can piece together evidence leading to those who killed the two British nationals," said the source.
Meanwhile, investigators detained Montriwat Tuwichian, 45, a younger brother of Mr Woraphan, after confirming Mr Montriwat is the Asian-looking suspect caught in security camera images a few hours before the two Britons were found dead on the beach on the morning of September 15.
Police began questioning him at 11am yesterday and released him three hours later, lacking evidence or witnesses to substantiate criminal charges against him.
However, Pol Lt Gen Panya, who participated in the questioning of Mr Montriwat, said police believe they have identified all the key people of interest.
Mr Montriwat runs the AC Bar where Witheridge and Miller were last seen on the night they were killed.
Pol Lt Gen Panya also confirmed that Mr Montriwat is the man captured in the AC Bar's security cameras.
"Please trust the authorities on this," he said. "We're not going to make anyone a scapegoat.
"This case really is a high-profile one and the rest of the world is watching. The police are working hard to cement evidence to prove the suspects guilty.
"Now the public is highly concerned about possible interference by local influential figures in the murder investigation.
"I insist that such people are no obstacles to the police's work in this case at all," Pol Lt Gen Panya added.
About an hour after he was detained for questioning, Mr Montriwat re-emerged from the investigation room for a toilet break.
As a crush of photographers moved in, he paused on his way back to the interview room to rail at them for taking his picture.
He said he was innocent and the true story would eventually come out.
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