Originally Posted by DChero
It's from the Empire interview. Here's the rest of the quote. I can see where you're getting the idea that this is meant to be the ultimate catalyst, but I don't take this as a primary reason (if that makes sense). He also cites the original ending being lackluster, puts a lot of story into Clark's parents (all of them) and there's the idea that adds to Zod's character, the "death by cop" quote.
Funny enough Zod never attemped to kill any humans up until that family in the train station.