The bodies identified to be of Maneswar Munda, Burha Teron, Bishoni Teron and Suren Kramcha, according to Sonitpur SP Sanjukta Parasar.
The hands were found tied and there were several wounds of sharp weapons, police said.
Locals informed the police after discovering bodies of the four, who were missing since January 29 last when 11 CPI(ML) supporters were killed and many others injured by miscreants from Arunachal Pradesh, they said.
The bodies were sent to Ketela Mission hospital here for postmortem, they added.
Following the attack an eight-day economic blockade against Arunachal Pradesh was launched jointly by several organisations on January 30 demanding punishment to the culprits.
In the Assembly on February 13 the Assam government had charged the Arunachal Pradesh government of carrying out "some activities and implementing some schemes" at Bihali area.