Ngawi Police chief Adj. Sr. Comr. Eddy Djunaedi said that police detectives were investigating the crime scene in search of evidence and questioning witnesses.
"We are investigating the motive of the attack," Eddy said as quoted by tempo.co on Sunday.
At least 10 members of the Kera Sakti School sustained injuries in the attack, four of whom were severely injured during the assaults that took place in two separate locations in the region; Kedungprahu village in Padas and Sekarputih village in Widodaren.
The pesilat were training when dozens of people wearing ninja attire assaulted them with sticks, bottles and stones.
Source: The Jakarta Post