A 61-YEAR-OLD man has been arrested on suspicion of planting an explosive device at the Phramongkutklao Hospital on May 22 that left 25 people injured.

Authorities yesterday identified the suspect only as “Wattana”, a former electrical engineer at the Electricity Generating Authority of Thailand (Egat).

The suspect was taken into military custody and interrogated at the 11th Military Circle command in Bangkok yesterday. He denied any involvement with the explosion at the military-run hospital, according to a source.

A search of the suspect’s home in the Ram-Indra area of Bang Khen district allegedly yielded four improvised explosive devices in PVC pipes “ready to be used”, according to another source in the investigative team.

The source said many integrated-circuit timers similar to ones used in the explosive devices that were set off in two previous incidents – outside the old Government Lottery Office building on Rajdamnoen Avenue on April 5, and in front of the National Theatre on May 15 – were found.

A wall clock with the image of former prime minister Thaksin Shinawatra was also allegedly found in the suspect’s house.

The search at the Bang Khen house involved more than 50 police and military officers, the Thai News Agency reported yesterday.

Searches also were conducted at 10 other locations in Bangkok and in surrounding provinces but no suspicious materials had been found, the police source said.

According to a source familiar with the investigation, Wattana was believed to be the man who took a fabric bag containing the explosive device concealed in a vase into the hospital’s waiting room where the bomb exploded. He was in the room for about 10 minutes before leaving without the bag.

Security camera recordings at the hospital showed the person of interest as a thin, long-haired man about 160 to 165 centimetres tall.

The explosion at the hospital was the third to occur in Bangkok within two months. The homemade bomb planted at Phramongkutklao Hospital exploded and injured 25 people on the third anniversary of the 2014 military coup that brought down the elected government of Yingluck Shinawatra, Thaksin’s younger sister.

After locating the suspect, investigators interviewed a woman close to him in Nonthaburi, who reportedly said that he did not like the military while having a strong political preference, according to the source in the investigative team.

The suspect was arrested on Wednesday evening while taking a bus home, the source said, adding that police were attempting to find out whether he had acted on his own or had been instructed by someone to plant the bomb.

He was charged with possessing explosive devices and materials used in the production of explosives. If there is sufficient evidence, police will also charge him with terrorism.

Deputy Prime Minister and Defence Minister Prawit Wongsuwan yesterday confirmed that authorities had arrested a suspect in connection with the Phramongkutklao Hospital explosion. However, he added that no connection had been established between the suspect and any group of dissidents in the military.

“The investigators are trying to find out if other people colluded with him in carrying out the attack,” said Prawit, who is in charge of security affairs.

He claimed that the suspect had confessed to planting the bomb, although that was contradicted by what a police source said.

Meanwhile, deputy national police chief Pol General Srivara Ransitbharamanakul said yesterday that the investigation into the explosion at the hospital “is progressing satisfactorily”.

He declined to confirm or disclose any details regarding the reported arrest of the suspect, saying that national police chief Pol General Chakthip Chaijinda would be the only one to talk publicly about the matter.