"The militant leader Sohan D Shira escaped, but security forces shot dead his PSO in an encounter," Inspector General of Police (operations) GHP Raju told PTI.
Acting on intelligence inputs on the presence of the top militant in the camp, special police commandos raided Shira's camp, but could not catch hold of him, but his PSO was killed in an encounter near Adugre village in the Durama hills range in the wee hours, he said.
A personal mobile phone of the militant along with grenades, explosives and GNLA documents was recovered from the camp, Raju said.
A search operation was launched in the jungle to trace the assailants.
Shira founded the GNLA in the fall of 2010 and since then the outfit was involved in kidnapping, extortion and killing of civilians as well as security forces.
The GNLA was also responsible in blowing off the head of a woman last month after she resisted an alleged molestation and rape attempt. The outfit later owned up to the killing of the 35-year-old woman alleging her to be a police informer.