It doesn’t matter as to who’s word vs. someone else’s word, what matters is conspiracy. That’s what played out when it came to Leo’s lawsuit against Sonny & Titan. Same here, Dimitri can verify who were witnesses to his shooting, he saw them when he was shot, Leo who just had gotten wind of Gwen & Kristin’s plans for revenge, once Dimitri names his witnesses to his shooting would put Leo in the catbird seat, he knows that all the party’s involvement with the fallout. He will learn as to who the witnesses are, he knows about Gwen & Kristin’s plans, the police have the weapon, then once they get the bullet, they will know that it didn’t come from the weapon that they had gotten, & that all three of them lied about the events in play & that it’s also known that Vivian isn’t staying long, you tell me, what better way to avoid of what is now in Leo’s hands is by telling the truth about the shooting, to prevent Leo from blackmailing all of them, don’t you think?