Wattana Pummares, 61, a former engineer at the Electricity Generating Authority of Thailand, said that his intention was only to convey his frustration about the coup and the military takeover of government.

“I wish to express my regret and convey my apologies to those affected by my acts, and particularly those injured,” he said at a press conference at the Royal Thai Police headquarters.

The event was held after the military handed Wattana over to police. He was charged in relation to three bomb attacks in Bangkok this year.

He insisted that he acted alone in all of the attacks, with the earliest traced back to 2007, but said he had nothing to do with letters sent to Bangkok hospitals warning about possible bomb attacks.

“I acted out of my frustration over the coup and the military’s participation in politics, not due to a political motivation. No politicians from any side were behind my activities,” he said.

He said he had attended gatherings of the now-defunct People’s Democratic Reform Committee and red shirts – only to understand both sides of the story.

All the attacks he committed were inspired by the same motivation, he said, after he saw the country damaged by coups and military figures take over the running of the country.

What he had done was a symbolic gesture of his opposition to the coups, Wattana said.

“Thailand’s reputation and economy has been damaged because of the coup d’etats that overthrow the elected government from time to time. The coups also violated people’s basic human rights. I, as a grassroots citizen, wished to tell the military governments that people do not support and agree with their seizure of power,” he said.

Every time he planted explosives, he said he tried to avoid possible harm to other people. He also corrected the media’s term that he planted “bombs”, saying he had used giant firecrackers.

Wattana appeared to be calm and refused to answer some questions posed by reporters, saying he had already given the answers to investigators.

He said he did not hate the military, and actually “loved” it, but he did not like some military officers staging a coup and taking over the post of the prime minister and the government.

“I wished that my case would be considered an example for the military to seek peace. I am confident that after this, the military and people will cooperate in order to seek a sustainable peace.”

He said he had received treatment respecting his basic human rights during his military detention after the arrest last week. The military arrested him under a junta order that empowers it to arrest and detain suspects.

National police chief Pol General Chakthip Chaijinda said at the press conference that police had spent more than 20 days after the hospital explosion investigating the case before detaining suspects.

Police had extended the investigation to determine if accomplices were involved, but for the time being Wattana’s confession had led the police to believe that he acted as a “lone wolf”, Chakthip said. However, he said police were ready to arrest more suspects if any were found to be involved.

Pol Maj-General Chayapon Chatchaidej, a crime suppression chief, said police believed that the suspect was indeed the bomber behind the attack at the old Government Lottery Office building, the National Theatre and Phramongkutklao Hospital this year.

That conclusion was supported by forensic evidence collected from the crime scenes, such as electrical switches, integrated circuit timers and wire connections, which had the “same signature”, he said.

Chayapon added that one of the important pieces of evidence was a selfie photo taken by a bystander at a Phramongkutklao Hospital room before the explosion, which showed a vase that was believed to contain explosives.

“From the photo, police could narrow down the time of the crime [when the vase was planted in the area], which led to the arrest of Wattana. Police have reviewed footage from more than 100 security cameras,” he said.

When the suspect was initially arrested, he denied the allegations. However, he confessed after military authorities searched his house and found explosive components such as IC circuits and the clothes he wore on the day of the hospital attack.