Demand a lawyer. The police are going to use unfair but legal tactics to get you to sign a statement. If, however, you ask for a lawyer, they must stop the interrogations and get one for you.
The only things the police cannot say during the interrogation is something in the form of a deal, or a threat.
They cannot say "If you tell us this....we will get you off the hook."
They cannot say "If you don't talk to us we will put you in a cell with this guy who will do this to you...."
Or anything similar. But again, they can legally use other scare tactics, and can even legally lie about evidence before you, such as saying they have your fingerprints when they really don't.
That is why you must always make use of your right to remain silent and demand a lawyer. A lawyer is the only person that can help you.
Remember that they CANNOT refuse to bring in a lawyer, all interrogations are video tapes with both visual and audio capabilities, and refusing to bring in a lawyer when asked is grounds for you to get off on a technicality.