I'm watching the same special.
Personally, I would have done something, anything I could think of at the moment with what I had to help another person. I hope someone would do that for me. If someone sat by idly and watched as my legs were ripped off, I'd be pretty mad. Even if they can't help, at least they tried.
If the other people had time to react, the man shooting the video should too (especially since he knew the girl and called out her name)
Also, this isn't being used for the anatomy of a shark bite because you don't see the actual bite, just the attack.
When people sit by and let these things happen things like the Kitty Genovese case occur
http://www.newsday.com/extras/lihistory/8/hs818a.htm).