INVESTIGATORS are convinced that political hardliners were behind Monday’s bombing at Phramongkutklao Hospital and the perpetrators are still in the country, national police chief Pol General Chakthip Chaijinda said yesterday.

“The investigation has progressed a lot. Police believe this incident was carried out by a political group bent on violence. They are extremists,” Chakthip said.

He added that 61 out of more than 80 witnesses had been questioned by investigators and at least five provided “very useful” information.

Meanwhile, Army commander-in-chief General Chalermchai Sitthisart yesterday said hardline red-shirt leader Wuthipong “Ko Tee” Kotchathammakhun could be involved in the attack.

He added that Wuthipong, who has been in exile in Laos, often campaigned for violent causes through social media.

“Ko Tee is just one of the suspects,” said the Army chief, in his capacity as secretary-general of the National Council for Peace and Order (NCPO).

But he declined to confirm speculation that pro-red shirt military officers were involved in planting the explosive device at the military-run hospital.

Police have come up with 20 suspects in the hospital blast after studying recordings from 17 security cameras at the scene, according to a source familiar with the investigation.

Metropolitan Police investigators were attempting to identify the suspects whose images were recorded on different security cameras inside the hospital, the source said yesterday. The investigative team was allowed access by the military to the hospital’s security-camera data centre almost 30 hours after the explosion, said the source, who spoke on condition of anonymity.

Police investigators determined that none of the cameras recorded when the vase containing the explosive was placed inside the room because the vase’s location was not covered by the single camera in the room, the source said.

Chakthip yesterday chaired a meeting of more than 200 police officers tasked with investigating the blast.

The meeting, held at the Royal Thai Police headquarters, lasted about 90 minutes.

Speaking after the meeting, the national police chief said he had ordered heightened police security at significant landmarks and symbolic locations, as well as at popular tourist destinations.

Police officers had also been sent to different hospitals in Bangkok to train personnel on how to improve their security measures, according to Chakthip.

He added that security had been heightened at Police General Hospital and many Special Branch officers had been dispatched to the police-run hospital to boost its security.

The national police chief has appointed his deputy, Pol General Srivara Rangsibhramanakul, to head the investigation into the hospital attack.

Following the order, 201 police investigators were assigned to join the investigation.

Deputy Prime Minister and Defence Minister Prawit Wongsuwan said yesterday that the explosion at the hospital was the work of “some people close to us”. He did not elaborate when |speaking to a reporter over the |telephone.

Prawit ruled out the possibility that insurgents from the southern border region were responsible for the incident, which left more than 20 people injured.

“There’s still no conclusion. But in fact, it’s none other than some people close to us,” he said.

In a related development, the junta is considering a revival of its order that empowers a military court to try security-related cases, following the explosions in |the capital, Chalermchai said |yesterday.

Chalermchai added that officials working on security matters suggested reviving NCPO Order 50/2557 following recent violent incidents.

“Let me stress that it’s in the process of discussion only. There has been no specific policy or order regarding this matter,” he said.

The NCPO order in question, issued just a week after the May 2014 coup, placed cases relating to firearms and explosives within the jurisdiction of military courts. It was rescinded by another NCPO order in September last year.