What Does True Repentance Require Of the Penitent?

I don't know, I'm asking.
Without reference to the details of the misdeed, the motivation, the perpetrator, or the victim in this case, the miscreant who visited an atrocity upon still surviving victims has been released from prison and says he is sorry.
He wishes his victims could “understand a bit better what motivated me and people like me”.

I think that is a heinous, self-serving thing to say, since it implicit invites a comparison between his putative sufferings and his victims actual ones.

An authentic apology would not.

However, my question is about something different - the victim says,

Well, he can say he’s ‘sorry’... but he hasn’t repented because he would know it meant going to the authorities and telling them all he knew of the identities of those who commissioned [his crime]. He was the monkey. Let him tell us about the organ-grinders. But he’s declined to do that.

Is that so?
Is offering up ones partners in crime sin, (who may or may not repent of the evil they have done and the grief they have caused,) a  requisite of true penitence?
Resolution to sin no more, yes, making of what amends one can, of course -- but informing on ones confederates?
And does the answer depend on whether the sinner still thinks his cause was just? or depend on whether the cause is/was just?