Lawyers for Ahmaud Arbery's family aren't closing the book on that mysterious note left at the shooting scene -- they've gone to cops with new information that could tie its author to the case.
Attorney Lee Merritt, tells TMZ ... he and his team of investigators received what they believe is a credible tip claiming the note's author is someone who shares ties to Travis and Gregory McMichael and/or William "Roddie" Bryan.
You'll recall, the note says, "Ahmaud, I am so sorry. I should have stopped them. I am so sorry."