My brother-in-law was murdered and I was wondering if he could end up teaching the man that did it in the post-life. If so, will he remember him doing that to him? I would also like to know if that man will ever be forgiven for that kind of a sin. Thanks.
First, can we remember in the spirit world the acts of mortality? Nothing that has ever occurred to us in mortality has left our minds. We may not be able to recall on command all that has happened to us, but under certain conditions all can be recalled. I imagine that in the spirit world there will be no inhibitions to our memory. Alma said,
Can ye imagine yourselves brought before the tribunal of God with your souls filled with guilt and remorse, having a remembrance of all your guilt, yea, a perfect remembrance of all your wickedness, yea, a remembrance that ye have set at defiance the commandments of God? (Alma 5:18)
If we will be able to remember all our guilt, we surely will be able to remember all the other thoughts and actions generated in mortality. So if your brother-in-law were to be in contact with the man who ended his mortal life, without a doubt he will remember what was done to him, and it is possible that he could teach him the gospel.
Whether or not the sin of murder can be forgiven I would imagine depends as much on the intent as on the act, and since we cannot see into the heart of man we are not in a position to make any judgement. We understand that there is only one unforgivable sin, as explained in the Doctrine and Covenants,
The blasphemy against the Holy Ghost, which shall not be forgiven in the world nor out of the world, is in that ye commit murder wherein ye shed innocent blood, and assent unto my death, after ye have received my new and everlasting covenant, saith the Lord God; and he that abideth not this law can in nowise enter into my glory, but shall be damned, saith the Lord (D&C 132:27).