Can Murderers Be Forgiven?

In my write-up today on Joseph Telushkin's A Code of Jewish Ethics, Volume 1: You Shall Be Holy, my post will be synchronic rather than diachronic, in that I'll discuss Telushkin's depiction of Judaism's stance on the issue of forgiveness without always identifying the different sources that he cites along with their times of composition.

I was somewhat confused about whether or not Telushkin believes that murder can be forgiven, according to Judaism. He cites a source saying that God ordained for David to commit adultery with Bathsheba and to kill Uriah----acts that were so uncharacteristic of David----in order to demonstrate to us God's willingness to forgive sinners (B.T. Avodah Zarah 4b-5a). That implies to me that murderers can be forgiven. At the same time, Telushkin states that murder technically cannot be forgiven, for the victim is no longer around to forgive the offender.

But couldn't God forgive the offender, even though the victim cannot? Telushkin cites a source saying that we should ask the person we offended three times for forgiveness, and if he still hasn't forgiven us, then that is his problem, and we are considered to be forgiven by God (Maimonides, "Laws of Repentance" 2:9). That seems to imply that God's forgiveness of us is contingent on others' forgiveness of us, at least to a degree. Why else would the source assure us that God forgives us, even if somebody else does not? There appears to be an assumption that God's forgiveness of us and others' forgiveness of us are linked somehow, even if this principle is not absolute.