Daryll DID set the whole thing up
I must have watched a completely different movie from the people on this board. I've seen posts saying Daryll had contact with the copy cat guy, but he wasn't running the show. I believe he was.
From what I saw in the end, we see Daryll writing a letter to someone, and the voice over says something to the effect that the last guy got carried away and went overboard.
I got the impression that Daryll hired the copy cat killer to kill Helen, but the guy got too wrapped up in the killings, rather then just go for Helen, he went way overboard. It seemed to me Daryll was writing to someone else to get that guy to finish the job, hence, kill Helen.
It seemed to me Daryll wanted revenge because Helen says at one point in the movie it was her testimony that put him behind bars. Daryll did orchestrate it.
Check your palates. Get them tested.