District and Sessions Court Judge Ashant Das acquitted the eight accused, who have spent over nine years in jail, due to lack of evidence against them.
Those acquitted were Ranjit Sana of West Bengal, Asutosh Soren and Rabi Dulai of Jharkhand, Kamalakant Sethy and his wife Chandrabati Tukuruka of Ranapur, Kishore Jena of Delang in Puri and Bikram Mallick and Sushil Behera of Aska in Ganjam district, said special public prosecutor Brundaban Panda.
They were also accused of being involved in the attack on Nayagarh police training school (PTS), Daspalla police station and Mahipur police outpost.
Fourteen people, including 13 police personnel, were killed, while 10 others injured in the attack. After looting the district armoury in Nayagarh, the heavily-armed Maoists had virtually laid siege to the town for several hours.
A huge cache of arms and ammunition was taken away in a truck and a bus by a group of nearly 100 Naxals, including women cadre, the police had said after the incident.