Although Wattana, 61, confessed on Tuesday that he planted the explosives over a 10year period because he wanted to express his frustration over the coups and the coup leaders, some people still doubt that he acted alone.

The bomb at the hospital exploded on the third anniversary of the coup led by General Prayut Chanocha, the present prime minister.

“The officers have to take a careful look whether the investigation into Wattana’s crimes was really complete to see if there were other accomplices helping him. We do not yet have confidence on the matter,” Prawit said.

Prayut on Tuesday said he believed that Wattana, a former electrical engineer, was a “lone wolf” attacker.

Prawit said that the premier was speaking from the evidence police have so far, but the investigation would continue.

Prawit denied that Wattana allegedly planted the bomb in a hospital room that was named after him because he wanted to express his frustration towards him personally. “The suspect told police that he picked the room [to plant the bomb], not because of the name but because there was not so many people there.”

Deputy national police chief Pol General Srivara Rangsibhramanakul has said he believed Wattana had accomplices to help commit the crimes.

He did not give further details.

Meanwhile, Wattana was taken by police to different locations yesterday to reenact his alleged preparation for the explosions.

Wattana, 61, wearing a mask and accompanied by dozens of police officers, appeared to be calm and at some locations he gestured with a Vsign to reporters and photographers who followed the event.

Wattana, a former electrical engineer of Electricity Generating Authority of Thailand (Egat), on Tuesday expressed his remorse and deep regret that his acts injured people. He confessed that his crimes were intended to express anger over the coup and coup leaders.

He was taken to a shop where he allegedly bought the vase that he hid an explosive inside to attack the hospital and another shop in a market behind Egat headquarters in Nonthaburi province where he bought a PVC pipe that he used as part of the explosives.

Wattana took police to a shop in the Banmor area where he allegedly bought other bomb components such as condensers, IC timers, batteries and switches.

In the reenactment, Wattana told police that he rode a bicycle to Soi Charansanidwong 96/2 before getting in a bus No 18 at about 7.43am and getting off in front of the hospital.

After he allegedly planted the bomb he used the same bus to go back to Soi Charansanidwong 97 to get the bicycle.