It was necessary to apprehend him.

I feel sad on several different fronts:
For the people who died, who were injured.
For the family of the bombers. (When there is mental illness, marginalization in a family to lead family member to kill others..., it would be upsetting to other family members)
For the death of the lst bomber ....which to me, looked close enough be to a suicide also.

As for the cheering and all that. It's the total opposite ..it's all of the above.