You will encounter the Blast Shard Bomber when doing the side mission, "The Gauntlet", located in Gas Works. Those blast shard bombs you constantly see planted all throughout the city? Yeah, he's the guy responsible.
You'll be forced to chase him down while he runs away while blowing up buildings with his bombs and whatnot. At the end of the chase, he'll lead you to some hostages and you'll corner him. You will be given the option to either defuse the bomb then restrain him, or shoot him and blow up the bomb killing him along with the hostages he's held up else up.
Be a hero and defuse the bomb, or laugh as you blow up the Bomber along with the innocents; choose either to complete the mission and unlock the trophy.