Piecing together the evidence collected so far, the anti-terror probe agency NIA said the total number of militants who participated in the attack was 23 out of whom two were killed on June four in retaliatory action by the Army in Chandel district of Manipur, official sources said.
Army trucks were attacked with 'Lathod guns' and grenades by suspected terrorists of NSCN (Khaplang), killing 18 soldiers and injuring 15 others in Moltung.
While some of the explosives cans were detonated, a few unused ones found later have been sent for forensic tests.
NIA has been able to make only one arrest so far in Khumlo Abi Anal, 40, a self-styled 'Regional Commander' of NSCN-K. He is alleged to have taken part in the conspiracy hatched for the brazen attack.
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During the investigations, NIA examined several surrendered militants of NSCN-K, who also helped them identify many of the accused.
NSCN(K), which walked out of a ceasefire agreement with India in March, has been involved in a series of attacks in tandem with some other militant groups in the North-East under the banner of 'United Liberation Front of South East Asia'.
NIA had registered a case under various sections of the Indian Penal Code, Arms Act and Unlawful Activities (Prevention) Act in connection with the incident.
The ambush, representing an act of waging war against the Government of India, is alleged to have been executed by armed formations belonging to the Nationalist Socialist Council of Nagaland (Khaplang) and its affiliates active in North Eastern states and along the Indo-Myanmar border region, NIA said.