DUP Secret Agents are one of the side missions in the game, where members of the DUP will masquerade as a normal citizen and blend in with the crowd. When you start this side mission, you will be presented with a picture of the person you’re looking for, and you have to find and kill them before they escape.
This is one of the trickier side missions/collectibles in the game, as the moment they spot you, the Secret Agents will take off. You will have to give chase and they are able to use a Concrete dash maneuver to make the chase even harder, usually leading you into an area with enemies. The trick is to spot them before they run off and blast them, if you can.
If you wait until later in the game, the Laser Focus upgrade for the Neon power will make it easier to kill them, as the slow-motion effect gives you more than enough time to hit the Secret Agents, even when they are running away.