People say we need to forgive those who have wronged us. But when does forgiveness actually occur?

I was thinking of the following situation. A man murders a college student. The murderer disposed of the victim's body in an undisclosed location. The murderer is sentenced to life in prison. The victim's father gets to a point where he has forgiven the murderer. Or has he? The father still pressures the murderer to disclose the location of his daughter's body so the family can get closure. Has the father truly forgiven the murderer? Should the father leave the murderer alone and not try to find the location of his daughter's remains?