The leopard entered the house of Haren Roy in Charaikhola village in Golokgunj area of the district and attacked him and two other family members.
Villagers assembled before Roy's house as family members raised an alarm following which the leopard escaped but was chased and later killed by the mob.
The villagers claimed that they had informed the forest department but its personnel reached the spot quite late and apprehending further attacks by the animal, they had no other choice but to kill the leopard.
The condition of Roy, along with Gopal Roy and Jatan Roy, was stated to be critical and they have been admitted to Dhubri Civil Hospital.