What he said. Unfortunately, also you might have more than just the one. I'd scour your tank for any others and then do it again. They will eat any smaller animals vertebrates or invertebrates that they can get their jaws on.
That video was disturbing. I am naturally a little squeamish so I forced myself to watch it. But I was just so sickened the poor fry had to live while his body was devoured. I can't imagine the excruciating pain.
Nature has no limits on its beauty nor brutality. Thanks for the link.