Nic I agree with those that say let's cut these people some slack because they are overwhelmed with grief at the moment and are falling back on their belief systems for comfort.
Having buried my parents and husband I have experienced something I really can't describe properly. When my mother died, we drove away from the hospital at dawn on a gorgeous May morning. The scenery looked so bright and the world seemed so beautiful, rabbits, pheasant everywhere and even a fox crossed the road. I remember thinking what a beautiful day. When my husband died something similar happened, I felt such love for everyone involved and I wanted to comfort them.
Yes it is probably caused by a brain chemistry change brought on by shock and grief that has survival value but there is something about acute grief that makes you feel what life is all about in those few days afterward. It makes everything so real, everything so poignant, relationships so important. Death makes everything else seem trivial.
So I agree it seems weird to say you forgive someone who has murdered your loved one and I feel sure I wouldn't feel that but what grief does to your brain chemistry plus their belief system might explain it.
As regards forgiveness, I don't understand the concept of forgiveness in the religious sense. I think we have long memories for things that hurt us because that's how successful species survive. We remember the things that cause pain, physically and emotionally. Is the grief reaction of these people normal? Probably, within their belief system.
Perhaps forgiveness has been the best we could come up with to help ourselves psychologically thus far in our development as a species. Now we understand the brain and the mind much more I don't think we need to necessarily forgive to recover from trauma and move on, there is therapy and more out there to help us.