You simply have to pick who gets the ID, the "cop" has nothing to do with it.
If you cracked Daria's computer (I think there might be some other way?) it leads you to an NPC (whose connection to Daria is hinted at throughout certain places in the game well beforehand if you pay attention very closely) who explains what's going on. You can convince him to tell you how to talk down Daria, and have a CASIE sequence against her instead of taking her down.
Yeah I did the ID for the old man and the objective marker is now pointing me towards the cop. Can I not just deliver the ID and finish the side mission?
It just tells me to deal with him.