Jakarta mosque blast: Teen suspect's diary reveals loneliness, online radicalisation behind attack

Jakarta authorities have unearthed new details in the investigation into the November 7 bombing at a school mosque , tracing how a 17-year-old student planned the attack largely in isolation. The teenager, hospitalised after sustaining injuries in the blast, is being treated as a minor under Indonesia’s juvenile justice system, as reported by Reuters.

Investigators recovered a 42-page diary from the teen, described as a “Diary Reb,” which offers a window into his mental state and motivations. The diary contained sketches of the mosque layout, notes on where to place explosives, and the date of the attack. Authorities say the notebook detailed feelings of loneliness, isolation, and a desire for recognition within extremist online communities.

Police reported that the teen acted alone, creating seven small improvised explosive devices, four of which detonated during Friday prayers. He reportedly learnt bomb-making techniques from online tutorials and was active in a Telegram group that glorified extremist violence.

Jakarta police spokesperson Reonald Simanjuntak said, “He wanted to be recognised by members of the online community … because he feels lonely.”

The boy’s family background reflects his isolation. He lived in a modest North Jakarta home with his father, who works as a cook, and several boarders. Following his parents’ divorce and his mother’s remarriage, he reportedly spent most of his time alone behind a laptop. Relatives said he had minimal social interaction outside his immediate household.

Authorities also discovered that he misled his father about the items he was buying online, claiming they were for cosplay purposes. Investigators are scrutinising his digital footprint alongside his personal materials, including the diary, to understand the motivations behind the attack. Officials believe the teenager’s actions stemmed more from personal trauma and a sense of alienation than from formal religious or ideological indoctrination.

Police are continuing their investigation to determine whether other people or networks contributed to the attack, while also deliberating on the appropriate legal measures given the perpetrator’s status as a minor.