The most important aspect of this decision has to do with our individual faiths.
We have to remember that from both a Jewish and a Christian standpoint, (Simon vs Karl) Simon is required to forgive and not hold grudges. In the bible, Luke 17: 3-4 says “If your brother or sister sins against you, rebuke them; and if they repent, forgive them. Even if they sin against you seven times in a day and seven times come back to you saying ‘I repent,’ you must forgive them.” and Judaism has the golden rule which states "You shall not take vengeance or bear a grudge against your kinsfolk. Love your neighbor as yourself: I am the
Lord"
The solution, however, is not that simple. The soldier had the wrong mindset to ask that of Simon. He believed that just because one Jew forgave him that he could rest at ease, when in reality that is not the case. Even if Simon forgave him, what he did impacted a group of people who are both dead and alive. People who Simon cannot speak for and others that could speak on their own but would have different views on the situation. In which case only God has the true ability to forgive Karl for what he has done. To quote Harry James Cargas, “If God chooses to forgive Karl, that's God's affair. Simon Wiesenthal could not, I cannot. For me, Karl dies unforgiven. God have mercy on my soul.”
What should Simon have done? Given that his faith tells him to forgive, even though he technically cannot do what the man is asking for. I believe that Simon should not have left the man without any explanation of why he would not forgive him. Every person deserves respect and happiness/relief on their deathbed in my opinion. I, Like Simon, would have been thinking about that moment for the rest of my life if I had left without an explanation.
In conclusion, I believe Simon could have left with an explanation of why he would not forgive Karl, But he was not obligated to do so. Jean Amery said “Don't trouble yourself, Mr. Wiesenthal. You didn't forgive and it was certainly your right, and if you had said words of forgiveness in a fit of emotion, that would have been legitimate too.”