Just. Demand. A. Lawyer. I cannot tell you how many times I have personally seen people NOT charged with anything despite being threatened and cajoled and even spending the night in jail or detention because they said nothing but demanding a lawyer over and over again.

You have to use your best judgment. Be polite Don't tell them your life story. Find out if they are charging you. See if they present evidence to you. If you're even near anything controversial ask for a lawyer. But read the room.