I'm not sure if we're seeing predation or molting. Either way it's a terrific shot. Especially since in my only encounter with a Katydid, it was already dead.
*CORRECTION 3-22-14: No sooner had I posted the original, than I got an update from Vandiveer who was visiting the Los Angeles Zoo. He showed the photo to an entomologist, who said it was a juvenile grasshopper who had just molted.
**CORRECTION 3-30-14: It's a Katydid. See post 3-30-14 for complete update. It's no surprise the LA Zoo entomologist was at a disadvantage, she was looking at Vandiveer's photo on his iPhone in bright sunlight.