In a major boost for the government and the state security forces, 20 top leaders of the tribal militant outfit All Adivasi National Liberation Army, including its chief Biren Gond alias Sanjay Lakra, have surrendered in Assam. Lakra, along with his comrades, surrendered at Bokajan in Karbi Anglong hill district of Assam on Sunday. The surrender of the top leaders of the outfit came after the recent arrest of its previous commander John Toppo in Nagaland.