Metropolitan Police Bureau (MPB) commissioner Kamronwit Thoopkrachang yesterday said that investigations into the grenade attacks on protesters on Banthat Thong Road and at the Victory Monument protest site had made progress.
He urged anyone who had information about the attacks to report to police.
A team led by deputy national police chief Pol Gen Ek Angsananon has obtained the identity of a suspected bomber involved in the attack at the Victory Monument.
The team also found the suspect was a member of the same group that carried out the grenade attacks on Banthat Thong Road and on Democrat Party leader Abhisit Vejjajiva's home.
The attacks had no links to police or the military, he said.
Deputy MPB chief Thitirat Nongharnpitak said grenades lobbed in Banthat Thong Road and at the Victory Monument had the same serial number.
This prompted police to look into past grenade attacks. They found that a total of 10 grenades from the same production batch had been used to carry out attacks here since 2006, Pol Maj Gen Thitirat said.
This type of grenade was not on the official list of weapons used by state agencies. The grenades were mostly used in communist countries. Russia manufactured this type of grenade but they could be acquired in neighbouring countries, he said.
Police were looking for a person who picked up fragments of the grenade on Banthat Thong Road after last Friday's bomb blast. They received the fragments from military officers who received the material from that person, Pol Maj Gen Thitirat said.
Meanwhile, Wuthipong "Ko Tee" Kotchathamakhun, a red-shirt leader in Pathum Thani, who has been accused of involvement in several attacks on protesters, was yesterday questioned by police.
Deputy city police chief Chayuth Thanathaweerat said Mr Wuthipong had contacted the investigation team on Wednesday and agreed to give a statement at the 1st Border Patrol Police Division, instead of the MPB as earlier planned.
During the interrogation, Mr Wuthipong insisted he had not travelled to Bangkok since the anti-government protests started. He was busy hosting his radio programme in Pathum Thani and had never been involved in any attacks, Pol Maj Gen Chayuth quoted the red-shirt leader as saying.
Pol Maj Gen Chayuth said the interrogation lasted for three hours.