The Phramongkutklao Hospital bombing suspect said he acted alone but authorities, including the prime minister, still have doubts.
The military on Tuesday handed Watana Pumaret, 62, to police for legal action.
Police held a news briefing at the Royal Thai Police office on the same day, with the suspect elaborating on the Bangkok bombings he reportedly confessed to, including the latest one at Phramongkutklao Hospital on May 22, the third anniversary of the coup.
A police presentation showed the suspect's alleged bombing records, focusing on the explosion at the hospital and the investigation leading to the arrest.
According to the presentation, Mr Watana took the bomb out of his car parked at the Electricity Generating Authority of Thailand (Egat) in Bang Kruai district of Nonthaburi on May 22. Then he rode a bicycle and took a bus to the army's hospital.
Once there, he reportedly stayed in the Wongsuwon dispensary room for an hour and a half, during which he allegedly switched on the timer of the bomb contained in a vase he brought with him. He walked out of the room 10 minutes before the explosion at 10.43am.
The suspect, who was a retired electrical engineer of the Egat, hanged around in the hospital's compound for nearly two hours before returning to Egat to take his car.
He allegedly made the bomb at his house in Bang Khen district and said he was responsible for five more bombings in Bangkok since 2007 because he hated a military regime and he acted alone.
However, the suspect reportedly said his bombs required circuits made by people with advanced technical knowledge. He did not elaborate.
Mr Watana allegedly said he did not intend to hurt anyone at the hospital, calling his bomb a big firecracker made with materials costing only 50 baht. Police said 28 people there were injured by pieces of the vase and the nails inside.
Mr Watana admitted a wall clock with a photo of former prime minister Thaksin Shinawatra found in his house was his and it represented his political affiliation.
National police chief Chakthip Chaijinda said evidence at hand showed the suspect assembled the bomb alone but detectives were finding if anyone else was involved.
Thai media reported Mr Watana's mistress was a red-shirt member in Nonthaburi province but police have yet to find proof of her connection with the bombings.
Police took him to some locations for re-enactment on Tuesday. The process would continue on Wednesday.
Prime Minister Prayut Chan-o-cha said on Tuesday that the suspect might have acted alone but unlike in other countries, a lone wolf in Thailand usually received support from some bigwigs.
Authorities are expanding the investigation to find suppliers of bomb components and take actions against all people involved.
Gen Prayut shrugged off the suspect's negative remark against the junta, saying he was focusing on solving the country's problems.
Suspected bomber Watana Pumaret, 62, (centre) stands next to bomb components allegedly seized from his house, with national police chief Chakthip Chaijinda (right) in a press conference at the Royal Thai Police Office in Bangkok on the recent bombing at Phramongkutklao Hospital. (Photo by Somchai Poomlard)
