Superintendent of Police Bhimsen Tuti said an assistant sub-inspector, a hawaldar and a constable of IRB were shot dead by a constable named Bikas Tiwary last night at Gurdari area of the district.
Tiwari fled with his rifle after the incident and the reason behind the incident was being investigated, he said.
The identity of the killed personnel was being established, he added.
Gumla is under Lohardaga(ST) LS seat.