Rey broke Undertaker's nose, cheek and reinjured his orbital bone (previous injury from 1995) with just one move. Devastating, and Taker had only just returned to the ring. A large portion of his face had already been reconstructed with metal. He might be a light and small guy, but these moves actually do hurt.
Here's a HQ version that's different from the one in the article
It looks like he was concussed when he got thrown to the outside, hit the apron, took a hit towards the ropes and choked while he waited for Rey to set up the 619. Ringside response was too slow, guy needed CPR not someone shaking him.
Doubt Rey will be charged with manslaughter, it was just an unfortunate accident.
I accidentally watched the video 
RIP to the other guy.
