
The arrested suspect has been identified as Sansern Sri-unruen, a Nakhon Pathom native, a police source said.
All seven suspects are now in military custody and will be handed over to the police by tomorrow, Metropolitan Police Bureau commissioner Lt-General Sriwara Ransibrahmanakul said.
Sriwara declined to identify the seven in custody.
Bangkok police are providing extra security at several locations that could be targets for future attacks, including certain communities and symbolic sites, he said.
“If any suspects resist arrest or fire at officers doing their duty, they will be dealt with sternly,” he warned, without elaborating.
Police are awaiting material from the military as additional evidence against the seven suspects.
He repeated an earlier police statement that the suspects were implicated by their use of RGD-5 hand grenades from Lot 57, which were used by attackers against the 2014 anti-government protest groups led by the People’s Democratic Reform Committee.
Russian-made RGD-5 hand grenades are not part of the police or military inventories, he added.
Sriwara said Sansern had not implicated anyone, as police had not questioned him properly and formally. He also said police had not summoned for questioning a retired Army general and a retired police lieutenant-general being mentioned in press reports because there is no clear evidence against the two men.
Police forensic evidence against the suspects involved in the grenade attack found links with two similar attacks earlier.
“These people are linked to each other, as the RGD-5 grenades were from the same Lot 57,” Sriwara said.