“You’re not a suspect. We just need you to help us understand what happened,” the investigator says. This is your chance, you think, to explain things and make the police realize that you did nothing wrong.
Except that the whole statement is probably a lie — and the police are absolutely allowed to mislead you or lie to you if they please. You can just about count on the fact that if a police detective says you aren’t a suspect but they still want to talk that you are, in fact, actually a suspect.
Getting you to talk before you’re actually under arrest is often vastly helpful to a prosecutor’s case. Many people mistakenly believe that whatever they say to the authorities can’t be used against them if they haven’t received a “Miranda” warning, but that’s not quite true.
The police are only required to issue a reminder about your right against self-incrimination if you are both in police custody and being interrogated. If you’re just having a “friendly chat” about the situation, you’re not officially in police custody and under interrogation.
Most of the time, if there’s a pre-arrest investigation going on, the police have already decided who is guilty (and it’s probably you). They’re simply trying to gather evidence that will strengthen their case. You will never talk them into believing that you’re innocent, and all the talking you may do just runs the risk of hurting your case if it winds up in court at some future point.
What’s the smart thing to do if you’re facing an investigation regarding a criminal matter? Ask for a lawyer and keep repeating the fact that you want to speak with your attorney before saying anything else until the investigators realize that you’re not going to back down.