Carlito's Way (two questions, no spoilers)

Why did Charlie have to lie to Vincent and company on his way out? Why didn’t he just tell the truth about how Vincent’s father and brother died? Or did his street instincts tell him they were, in any case, going to kill him or at the least delay him from his train?

Concerning his lawyer Dave Klienfeld, we know Charlie owed him his freedom. But Dave was ultimately Charlie’s downfall; regardless of whether it was Vincent who killed him, or Benny Blanco. What do you call a character like that, the kind who holds your fate, regardless of what you do?

Charlie couldn’t say that he was there while Kleinfeld murdered them. Well, he could have, but, to say that would implicate him as an accessory-not something that Mob guys would overlook too readily. What gangster would believe “Hey, I was there while they were being murdered…but, I didn’t help murder them. I was as shocked as you are” ?