Mission 4: Under Watch | Keys DMC: Devil May Cry Guide

KEY 1/2 (ARGENT) - You can find the key in the alley, just after you've destroyed the first camera. To get it, you need to use Eryx on the wall with red mark.

KEY 2/2 (GOLD) - Key is on one of the roofs next to the Divinity Statue. First use Angel Boost then Angel Lift to get onto a roof. Then go through small room and few corridors.