Two personnel of the Border Roads Organisation were killed and another injured as National Democratic Front of Bodoland insurgents fired at them in upper Assam's Dhemaji district, on Monday night.
A three-member group of the militants fired at the BRO camp at Sapori when the staff had retired after dinner, sources said on Tuesday.
One of the ultras, armed with an AK-47 rifle, waited outside while two others went in and fired at random, killing operator Pritam Chand from Jammu and Kashmir and driver Priyam Chand from Himachal Pradesh.
Bhisan Das from Jammu and Kashmir was injured after being hit by a rifle butt, superintendent
Eight persons have been picked up for questioning.
The NDFB, active in the area, had given an extortion note to the BRO in December, threatening to kidnap high officials if its demands were not met, the BRO men in the camp told the SP.
Saikia said had the BRO officials informed the police about the extortion note, security measures could have been tightened and the incident avoided.
Security around the BRO camp and its other settlements engaged in national highway construction across the state have been beefed up, official sources said.