This seems very strange... I realize you can reach some pretty high speeds, but I'm surprised that three people were injured so badly that two are dead and one is still in the hospital.
I'm wondering where on the black diamond they were stopped. That could shed a lot of light on what happened.
Just a reminder for everyone to play it safe out there. No matter how cool you think you look, it's not worth anyone's life (even if they technically were at fault).