JAKARTA, Indonesia — Indonesian police seized explosive powder and writings from the home of a 17-year-suspect in an attack on a mosque at a high school that injured scores of students, and are investigating his possible links to hate groups, officials said Saturday.

The suspect was among the 54 injured in Friday’s blast in Jakarta and was still recovering at a hospital, said National Police Chief Listyo Sigit after visiting him and the victims. The suspect was one of two students having surgery for injuries from the blasts.

“The suspect’s condition has improved, and hopefully this will make it easier for us to question him after he recovers,” said Sigit, adding that police currently only have one suspect. “However, we will not stop here. We will continue to investigate whether other individuals or groups were involved.”

At least two loud explosions occurred around midday at the mosque, just as the Friday sermon started, at SMAN 72, a state high school within a navy’s residential complex in Jakarta’s northern Kelapa Gading neighborhood. It prompted worshippers to flee as gray smoke filled the mosque.

The type of explosives used was not immediately known but the blasts originated near the mosque’s loudspeaker, said Jakarta Police Chief Asep Edi Suheri.

Most of the victims standing close to the loudspeaker lost hearing from the blasts and about 29 students remained hospitalized on Saturday for burns and other injuries.

Police said Friday they recovered a toy submachine gun belonging to the suspect and inscribed with what appeared to be white supremacist slogans and the names of two neo-Nazis convicted of deadly attacks in Canada and Italy.

Police ruled out a terrorist attack, and confirmed they were looking into reports in local media that the suspect was a grade 12 student who had been bullied and wanted revenge by carrying out what was intended to be a suicide attack.