Police suspect the gunmen who shot dead two highway police and a police assistant in Pattani on Friday night are the same group who killed four soldiers in Mayo district last year.
Pol Lt Col Narawee Binwaearong, deputy superintendent of Sai Buri police station, yesterday led a team to comb the site of Friday's attack on Pattani-Narathiwat 43 Road in Ban Karubee.
They found seven more 5.56mm and 7.62mm bullet casings, which they believe were fired from M-16 and AK-47 rifles.
More than 20 casings were also recovered from the scene on Friday.
Investigators believe the gunmen are from two insurgent groups led by Madari Tayae and Manang Bueraheng.
The groups are linked to the murder of four soldiers in Mayo district last year. They said the insurgents regularly use Toyota Vigo pickups to launch their attacks.
The brutal Mayo district attack went viral after it was clearly captured by CCTV cameras.
The footage showed 16 armed militants riding in three Vigo pickup trucks unleash a barrage of bullets at six soldiers patrolling on motorcycles.
Four of the soldiers were killed instantly while the other two were wounded.
Bullet casings from Friday's attack are now being examined to see whether they match with those from the Mayo ambush as well as any other past shootings, police said.
Friday's attack took place when Pol Sen Sgt Maj Worawit Kaewsrion, the 43-year-old chief of Kalapor highway checkpoint in Sai Buri, along with his deputy, Pol Sen Sgt Maj Pathompong Tosamart, 51, and Leejae Sulong, a 63-year-old checkpoint caretaker, were travelling back to their post in a highway police car.
Six people riding in a Toyota Vigo are then believed to have fired at the moving police car, causing it to swerve off the road and crash. Three gunmen then fired at the car from close range before fleeing, police said.
Meanwhile, a man was killed by four suspected insurgents riding on two motorcycles in Pattani's Yaring district yesterday.
Muhammad Mama, 31, and his wife were attacked on a road in Ban Jeh Oh in tambon Manag Yong. Muhammad was shot and later pronounced dead in hospital. His wife escaped unharmed.