Itanagar, Nov 12 (PTI) An India Reserve Battalion (IRBn) personnel deployed at Rajiv Gandhi University (RGU) in Doimukh, near here, shot dead one of his colleagues, police said on Saturday.The accused, head constable of 2nd IRBn Diyun, Wangru Taidong fired two rounds with his service rifle at constable Chingri Momai, reportedly after a heated argument on Friday night, Doimukh police station officer in-charge Inya Ete said.Ete said Momai was rushed to the Tomo Riba Institute of Health and Medical Sciences (TRIHMS) at Naharlagun, where he was declared brought dead by the on-duty doctors.We are investigating the motive behind the shooting, Ete said while dismissing the theory that the accused was mentally unstable.If he was not in a proper mental state, he should not have been in service, Ete said.The OC said that a police team visited the site and seized the weapon along with two empty cases and 28 live rounds.The body of the deceased has been kept at the mortuary of the RKM Hospital, here the OC said.He said an inquest and post-mortem will be conducted.Police said a case under Section 302 IPC (murder) has been registered in this connection and investigation started. PTI UPL RG