A policeman deployed at the Haiderpur water treatment plant here shot dead his three colleagues on Monday and later surrendered, officials said.
The accused, Prabin Rai (32), and the three deceased were Sikkim Police personnel deployed at the plant for its security as part of the Indian Reserve Battalion (IRBn).
A senior official said they received a PCR call at the KNK Marg Police Station at around 3 pm about the firing.
"Upon reaching the spot, it was found that three persons belonging to Sikkim Police had been shot, of which two had died on the spot and one was critically wounded and transferred to BSA hospital where he was declared brought dead," a senior official said.
He said the accused surrendered at the Samaypur Badli police station.