An Assam Rifles jawan allegedly clubbed his five-year-old son to death and seriously injured his 31-year-old wife at Seling village, about 40 km from here, police said on Monday.
The incident took place when 36-year-old Thangboi, who was on leave, returned to his home in the village.
He is posted in Tripura, police said.
His son Isaac Lalremruata, who sustained multiple injuries including head wounds, died on the way to a nearby primary health centre, they said.
Thangboi's wife Rosy Lalnunsangi was rushed to Aizawl and is being treated at the civil hospital where doctors stated her condition as critical.
The accused was caught by local people and handed over to the police at Bawngkawn police station here, they said.