Authorities on Wednesday arrested and identified the suspect only as “Wattana”, a former electrical engineer at the Electricity Generating Authority of Thailand.

According to a source, the suspect said he did it to hurt the military as they cracked down on the red shirt protest in May 2010.

Wattana had visited the hospital several times since April to plan the explosion, the source said.

The suspect also confessed that he was behind the bombs at National Theater in May 15 and in front of old Government Lottery Office on Rajdamnoen Avenue on April 5, as well as several incidents in 2007.

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

The source said many integrated-circuit timers, similar to ones used in the explosive devices that were ignited 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 suspect was taken into military custody and interrogated at the 11th Military Circle command yesterday.

Authorities will seek an arrest warrant for Wattana for having an explosive device in his possession without permission and carrying out an action that harmed others and attempted murder.

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.