Not knowing the content of the video, and assuming there isn't some additional crime that needs to be prosecuted, it's better to let it go. These events are traumatic not just for those who were close to them but anyone who experiences them later.

Through journaling and meditation I've seen how exposing myself to stuff like this causes echoes in the form of random associations, bad dreams, and poorer sleep. I was glued to this when it happened and still think of it often but it has added nothing to my life.

Many people cannot forget, but the rest of us can choose not to create such memories in the first place. 2 hrs? 15 mins? In the cases of terrorism, I recommend zero.