Six suspects are questioned in the police interrogation room. The suspects give the following statements.

Suspect 1. "One of us is lying."
Suspect 2. "Two of the six of us are lying."
Suspect 3. "I've seen what they've done and I know that three of us are lying."
Suspect 4. "Don't listen to a word anyone else is saying. Four of us are lying."
Suspect 5. "Let me go. Only five out of six of us are lying."
Suspect 6. "All of us are lying and we deserve to be incarcerated."

Only the suspects who are telling the truth will be released. How many suspects should the police let go?