So the police during questioning can lie and falsely tell a suspect that his friend (and co-defendant) has confessed to the crime, incriminating both of them. The cops can lie and falsely tell a suspect that his fingerprints or his DNA were recovered from the scene of the crime. They can even lie and falsely tell a suspect that they have satellite images that incriminate him. No court has ever held, as far I can tell, that police have a duty to tell a suspect the truth about the evidence they may or may not have against him.
This accurately states the law for police interrogations. But.
But many courts have identified legal distinctions between police lies about facts — i.e. “your buddy just ratted you out” — and police lies about legal rights. So the police are not supposed to tell a suspect during interrogation that any incriminating statement he says won’t be used against him. Or that what he says will determine the nature and degree of the charges. A cop cannot promise to get a suspect a reduced charge or sentence, decisions that are not in police hands.
In my experience, its implied promises which are mostly used.
Accordingly, DO NOT TALK. ANYTHING YOU SAY CAN AND WILL BE USED AGAINST YOU. YOU HAVE THE RIGHT TO REMAIN INNOCENT.