At the beginning of mission 3 The Escape, you will encounter Zeke, where you plan to go across the bridge. You are given here, the option of how you plan to break through the guards standing in your way, either by making yourself known, or hiding behind the nearby protesters and attacking the guards that way.
For Evil Riot, you will want to be hidden amongst the protesters when you fire you lightning bolts at the guards, earning a evil karma boost (for using the innocent people as a shield you fiend) and the trophy soon after.