What a confusing day 
I was going to suggest Dexter, wonder if they ever watched it? Over the course of the series he shows several people how build a 'kill room' (basically, a plastic cave) and get rid of DNA evidence. He also gets rid of bodies by chopping them up, and meticulously wrapping them in plastic. (Sorry! No nice way to write it
)
However, if that's the case, why leave all the blood and DNA at Becky's home? Surely they had time to clean up before AG got home?

Agreed and scenes from Dexter spring to mind.
I was going to suggest Dexter, wonder if they ever watched it? Over the course of the series he shows several people how build a 'kill room' (basically, a plastic cave) and get rid of DNA evidence. He also gets rid of bodies by chopping them up, and meticulously wrapping them in plastic. (Sorry! No nice way to write it

However, if that's the case, why leave all the blood and DNA at Becky's home? Surely they had time to clean up before AG got home?