One of the three bombs injured 27 people, including a young girl.
Police said the Nakhon Si Thammarat-registered bronze, silver grey Isuzu pickup truck used to conceal the carbomb that exploded near Oliver Hotel, the first of the three locations hit by the bombers, had been belonged to one of the people slain in an attack in tambon Thakamcham of Pattani's Nong Chik district on Dec 3. It was then stolen.
The pickup’s licence plate number was Bor Mor 5164, said police investigators at Sadao police station.
Police are focussing their attention on three key leaders of insurgent groups active in four districts of Songkhla -- Abdultorlae Kasor, Seree Waemamu and Ruslan Baima.
Abdultorlae is a suspect in the bombing of a tea shop in Na Thawi district in June and is wanted in 13 other cases. Seree and Ruslan are wanted by police in connection with a car bomb attack at Lee Gardens Plaza Hotel in Hat Yai in March last year.
Police said the improvised explosive devices (IED) used in the attacks on Sunday were all connected to alarm clocks. At least five suspects were behind the attacks.