A pickup truck from which assailants opened fire on a municipality office in Pattani's Khok Pho district on Thursday had been stolen from Thepha district of Songkhla, authorities say.
The dead body of the man who owned the truck was found yesterday, they said.
The gun attack on the Magrood Tambon Municipality Office (TMO) in Khok Pho district left four people dead and six injured.
A local intelligence unit said the vehicle used in Thursday's attack was stolen from Anan Kwanjun. Anan used the truck to take students to Theppittayapanumas School in Thepha district of Songkhla.
The assailants stole the pickup early on Thursday morning, held Anan and forced him to drive the vehicle to Khok Pho district of Pattani where they attacked the TMO before noon on the same day. After the incident, the attackers fled, taking Anan with them.
His relatives worried about him and sought help from police.
Anan turned up dead in Thepa district yesterday. His body was found by local police and investigators from the 43rd Border Patrol Police Unit in Thungdon canal in the district, which borders Pattani's Khok Pho district.
Authorities said Anan had been thrown from Ruamjaipak Bridge into the canal. An initial autopsy found his head and face had been hit with a hard object. His skull was fractured.
Meanwhile, a bomb targeting a military patrol exploded by rail tracks in Narathiwat's Rangae district yesterday morning, disrupting 14 train services on the southern line to Sungai Kolok district.
The bomb went off near Tanyong Limo railway station at kilometre marker 1104 about 6.30am. No one was injured in the blast.
The patrol discovered that 20 metres of track had been damaged. The explosion left a crater about 1m deep and 3m wide. Pieces of a 25-kilogramme cooking gas cylinder and a radio communication device were found scattered at the scene.
Sgt Dutsadee Khongpat, head of the patrol, said his unit, comprising six soldiers and three civilians, was patrolling by the rail tracks before a passenger train travelling between Sungai Kolok and Surat Thani was due to pass. The assailants triggered the bomb just before his patrol reached the spot, he said.