The assailants pulled out Birsa Bhagat (65) and his two sons, Bichar and Tara (25 and 22 years respectively) from their home at Khaira village and struck them with axes till they died, Sub-divisional police officer Chandan Kumar Sinha told reporters here.
Prima facie, he said the incident related to witchcraft.
Gumla, about 100 km from state capital Ranchi, is one of the districts in Jharkhand where the superstition of witchcraft claims at least one victim on an average every month.