Complex sentence: The other one, a Croat, rejects his friend's offer to gain an escape from the city; instead, he becomes a marksman in the ARBiH and attempts to counter the sniper threat.
Split into simpler sentences: The other one, a Croat, rejects his friend's offer to gain an escape from the city. Instead, he becomes a marksman in the ARBiH and attempts to counter the sniper threat.