Skull is found in the farmstead to the west of the Freedom base in the Army Warehouses, leading a group of seven Tunder S14-equipped Exoskeleton-clad experts.
If the player refuses to come along in the raid, Skull's team will attack the Freedom base by themselves and attempt to kill Lukash. In fact, siding with them boosts their reputation with Duty. Voronin advises the Marked One not to take part in their 'suicide mission,' but the player can still work for him with no damage to their reputation with Duty.
However, he disobeyed General Voronin's orders respecting the fragile ceasefire pact with Freedom and assembled his men for an ambitious attack on the rival faction's base. Skull was originally a member of Duty, holding the rank of colonel.