So a detective has called you up and invited you down to the local police sheriff’s department for an interview? When you arrive they will tell you that you are free to go at any time, and that they just want to get your side of the story. THIS IS A TRAP. Here’s how it works.
First, they only tell that you are free to go so they do not have to Mirandize you. You have to be under arrest and/or in custody for your Miranda warnings to apply. By telling you that you are free to go, they can ask whatever they want without telling you about your right to remain silent, or right to end questioning, or right to have an attorney present. They do this because the do not want you to have a lawyer there. They want to trick you into confessing.
Second, the “get your side of the story” line is meant to diffuse your anxiety. The detective wants you to think that they are going to help you and that they have an open mind as to what you tell them. Here’s the deal, before you show up the detective has already decided if they think you are guilty. Nothing you say will change their mind. They are going to take parts of your story that fit their theory of how are you guilty and assume those are true, they are also going to assuming you are lying if you make statements that don’t fit their theory that you are guilty. It is a lose-lose situation.