"Investigators are currently conducting a crime scene investigation at the detention center located inside Mako Brimob to find evidence," Iqbal said.

He said investigator had already found several firearms and glass shards.

"We suspect that the terror convicts used the shards [against] our fallen colleagues," he said, adding that investigators had also found several rifles and handguns.

The investigation is ongoing, but early indications suggest that the prisoners seized the killed officers’ weapons and obtained more by breaking into the evidence storage.

The Islamic State (IS) previously claimed that prisoners involved in the riot were its "fighters", but police continue to deny any connection.

"There is no strong evidence [of a connection to IS] based on the statements of several wounded officers and terror convicts, but we will continue to investigate this," Iqbal said. "So far, we believe the incident was triggered by a dispute over food."

The 155 inmates were transported to Nusakambangan prison in Central Java shortly after they surrendered early Thursday morning. (swd)