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recent foiled terrorist attack in Surabaya, East Java, was related to a vicious bomb attack on Jl. MH Thamrin in Central Jakarta in January, according to the National Police.

National Police spokesman Insp. Gen. Boy Rafli Amar said the planned Surabaya attack was related to the Thamrin bombing and inspired by the teachings of the Islamic State (IS) organization that spread through social media.

“The Surabaya terrorist suspects are linked to the Sarinah attack through Shibgho, who was seen at the scene when Thamrin bombing occurred,” Boy said on Thursday.

The police arrested three suspects on Wednesday, identified as Priyo Hadi Purnomo, Jefri Rachmawan, and Feri Novendi, who are all Surabayans. They were once imprisoned in Porong Penitentiary in Surabaya, where they shared terrorism ideology.

Priyo was imprisoned for a drug crime and released in 2015. Jefri is on the Porong Police’s wanted list for gang violence and domestic violence.

According to Boy, the police were finally able to arrest the three after years of closely monitoring Priyo in particular after he often visited Shibgho — a former convict responsible for an attack on a CIMB Niaga Bank in Medan, North Sumatra, in 2010.

“Like the Thamrin attack, the suspects in Surabaya were also planning a suicide bombing,” said Boy.

Soon after the arrests of the three suspects, the East Java Police’s bomb squad detonated the three bombs on Wednesday. The bombs were initially meant to be detonated in areas around downtown Surabaya, apparently to replicate the Thamrin bombing.

The first bomb was man-made and designed to be detonated by cell phone. The second was a pipe bomb, while the third one was a high explosive bomb designed to be detonated by a light sensor.

“The third bomb could only be activated once hit by light. It has relatively high explosive power that could cause extensive damage,” Surabaya Police chief Sr. Comr, Iman Sumanti told reporters on Thursday.

He said during the raid, Densus 88 counterterror agents found 23 bombs. While three were assembled and detonated by the bomb squad, the remaining 20 were in various stages of assembling.

The whole bombs and materials were seized from three separate locations: Jl. Lebak Timur 3D No. 18, Jl. Lebak Jaya III No. 88 and Jl. Kalianak No. 55. Besides the bombing materials, Densus 88 also seized two rifles, a pistol, four bullets and a computer kept in two boxes, one laptop, one multimeter, cash and two cell phones.

Terrorism observer and lecturer at the School of Social and Political Sciences at Malikussaleh University in Lhokseumawe, Aceh, Al Chaidar, urged the government to impose stricter punishment on terrorist suspects to prevent the spread of terrorism nationwide.

“Prison sentences should be stiff; a sentence involving the amputation of key parts of perpetrators,” said Chaidar, a former member of the banned Islamic State of Indonesia (NII).