A red-shirt guard Pichet "Phumkitti" Sukjiddathong has been arrested on suspicion of involving in the violent riots, classified as terrorism, Metropolitan police officer Colonel Songpol Wattanachai said on Tuesday.
Pichet, seen as the right-hand man of the late Maj General Khattiya "Seh Daeng" Sawasdipol who was the de facto leader of the red-shirt guards and succumbed to a gunshot wound in the head on Monday, was spotted at Soi Samsen 6 in Dusit District before his arrest.
Investigators are interrogating Pichet at a detention centre, located inside the Border Patrol Police Region 1 headquarters, Pathum Thani.
Pichet is expected to shed light on the organisational structure of armed red agitators.
In a related development, police have seized about 9,000 used tyres, believed to be destined for the red shirts to burn and cause mayhems.