When in Clocktower, bum rush the sniper, weapon slide away if you please (X+A while running) and get to a safe position.
Make sure you switched your shotgun with the rifle, because you will want your lancer.
Then go to the two sandbags that have the Hammerburst inbetween them.
Superjump one of them and land on the other (A+B), then you will land on top of the sandbag.
From there make your way to the median of the top of the level.
There will be a tree in your way, but it is no obstacle, just walk on through.
From there you have a clear shot at any victim roaming around down by the cars, 'nades, and boomshot.