The Big Picture at boston.com recently commemorated the twentieth anniversary of the Rwanda genocide in which the Hutu killed over a million Tutsi and Hutu sympathizers. A couple of images were particularly striking, but it was the stories (or perhaps story?) behind them that really moved me.

A study in contrasts: a man’s left hand and a woman’s handless arm. The caption provided details:

Emmanuel Ndayisaba, left, and Alice Mukarurinda, recount their experiences of the Rwandan genocide at Alice’s house in Nyamata, Rwanda Wednesday, March 26, 2014. She lost her baby daughter and her right hand to a manic killing spree. He wielded the machete that took both. Yet today, despite coming from opposite sides of an unspeakable shared past, Alice Mukarurinda and Emmanuel Ndayisaba are friends. She is the treasurer and he the vice president of a group that builds simple brick houses for genocide survivors. They live near each other and shop at the same market. Their story of ethnic violence, extreme guilt and, to some degree, reconciliation is the story of Rwanda today. The Rwandan government is still accused by human rights groups of holding an iron grip on power, stifling dissent and killing political opponents. But even critics give President Paul Kagame credit for leading the country toward a peace that seemed all but impossible two decades ago. (Photo by Ben Curtis)

How could they become friends after something so unspeakable? I was at a loss until I saw the next picture.

Its caption:

Mukarurinda Alise, 43, lost all her family members during mass killings in the 1994 genocide, but says she is now living with the man who hacked her wrist off. Alise forgave the man who she says went to the same school as her, after he came back and begged for forgiveness after serving time in jail for his crimes during a three-month killing spree in 1994 They are now married and living in Nyamata. (Photo by Noor Khamis)

It’s one thing to reconcile with someone who did this; it’s quite another to marry him. Then I looked closely at the names:

• Alice Mukarurinda
• Mukarurinda Alise

It’s the same person, and according to most accounts, she and her attacker are only friends. The thought that she could marry the man — inconceivable.

The forgiveness itself is difficult to understand. I try to imagine how the dynamics in such a friendship must work, and I can’t. I can’t even understand how Mukarurinda could consider forgiving the man who hacked off her hand and killed her child.

What is the nature of forgiveness then? What does it mean to forgive? At a party in southern Poland more than ten years, I had a long conversation with someone about this, and we came to the conclusion that it means not to forget, for that’s impossible, but merely not to hold it against the person, not to assume that the person will do it again — indeed, to trust that the individual won’t do it or anything similar again. Yet Ndayisaba himself admits that he feels such an atrocity could happen again. Would he be on the right side this time? Would he defend Mukarurinda this time instead of attacking her? That, I suppose, is exactly what Mukarurinda is counting on when she says she forgives Ndayisaba .