At least 54 people, mostly students, were injured in two explosions that disrupted Friday prayers at a mosque within a high school complex in North Jakarta's Kelapa Gading neighborhood.
The incident occurred around midday, just as the sermon began, sending worshippers fleeing amid thick smoke and shattered glass.
Authorities quickly identified a 17-year-old male student at the school as the prime suspect, who sustained injuries and is undergoing surgery.
Indonesia's national police chief, Listyo Sigit Prabowo, confirmed the suspect's involvement and stated that investigators are delving into his background, home environment, and potential motives.
Police recovered a toy submachine gun near the mosque, inscribed with what appeared to be white supremacist slogans referencing the 2019 Christchurch mosque massacre in New Zealand.
Prabowo noted that the device, along with other toy weapons and writings found at the scene, is being examined to clarify the perpetrator's intentions.
Jakarta police chief Asep Edi Suheri reported that the blasts originated near the mosque's loudspeaker, causing burns, shrapnel wounds, and hearing damage among those closest to the source.
An anti-bomb squad secured the area, finding no extensive structural damage to the mosque, though broken windows and debris scattered across the school grounds.
Investigators are exploring reports that the grade 12 student may have been motivated by bullying experiences, potentially planning a suicide attack as revenge.
Jakarta police spokesperson Budi Hermanto emphasized that while these factors are under review, challenges persist in gathering witness statements due to victims' medical needs.
Trauma counseling is being provided to affected students and teachers, with the capital's security described as stable.
Witnesses described chaotic scenes, with students in uniform sprinting across the basketball court, some clutching their ears against the deafening booms.
Relatives converged on hospitals like Yarsi and Cempaka Putih, anxiously awaiting updates on loved ones treated for injuries including head, hand, and foot wounds from sharp nails and blast fragments.
Of the 54 injured, 33 remain hospitalized, three with serious conditions, though no fatalities have been reported.
Authorities have urged the public to refrain from speculating about terrorism, stressing that a thorough probe will determine the full circumstances.
The deputy house speaker, Sufmi Dasco Ahmad, visited victims at the hospital and confirmed the suspect's age and status without further elaboration on motives.