This is achieved on the chapter Highway 17.
After treading through the cliff side roads in your buggy you will come across a rather large pile of crashed cars and a semi-truck on the road. To the right will be a grassy hill with a dead resistance member. Next to his body is a Crossbow, some bolts, and some supply crates. Make a quicksave here in case you accidentally miss.
Take the Crossbow and zoom in to see a billboard off in the distance. There should be a combine sniper perched on this billboard. Aim a little above his chest to compensate for the drop and the bolt should pin him to the billboard.
