This is very unfortunate incident happened in Outing village of Mon District of Nagaland in which 6 unarmed local Konyak Naga tribesmen were shot dead by the personnel of Assam Rifles .As per local Naga people the Assam Rifles personnel are fully responsible for this .

How can they kill unarmed persons ?

Their viewpoint  prima facie seems to be correct as the Assam Rifles personnel killed 6 unarmed  persons  coming from their work in backside of a truck .
In retaliation the villagers got enraged and attacked the Assam Rifle post in Mon District of Nagaland, in which 8 more civilians were killed and also one person of Assam Rifles too was killed in exchange of fire .
Assam rifles personnel unfortunately a native of Uttrakhand   was killed only in retaliatory action not in the initial stage when Assam Rifles personnel killed innocent unarmed civilians . 
This is the worst thing happened to Assam Rifles known as " Friends of the people of North East " now after this incident Assam Rifles  become from Friends to Fiends  .
It will take long time for The Assam Rifles to regain the faith of the local people of North East.With this incident a vociferous demand has come up to revoke AFSPA ( Armed Forces Special Power Act ) not only in Nagaland but wherever it is enforce in North East India .Even the Chief Minister of Meghalaya Conrad Sangma through a tweet demanded the revocation of AFSPA. Two enquiry committees have been set up one by the Indian Army and another by the State Government of Nagaland to probe this incident in which 15 deaths had taken place .We may be able to know exactly what had happened once the reports of these inquiries is made public within one month as promised by Union Home Minister Mr Amit Sah