In my experience, subjects of criminal investigations rarely help themselves by speaking to prosecutors or testifying before a grand jury. Far more often, they hurt themselves by falling into a perjury trap carefully set by prosecutors.
When prosecutors invite a subject to talk to them, they are not trying to help the subject. They are trying to bolster their case against him. Subjects can become targets and then defedants even if they tell the truth.
They can fill gaps or make statements that are contradicted by other witnesses who the prosecutors chose to believe. That is why, in my half-century of practicing criminal law, I have never advised a client to speak to prosecutors unless the alternative is worse.