Why were Wakefield and his accomplice keeping Jimmy alive?

I always thought it was because they wanted to keep it as a bargain token with Abby and to make it turn against her (besides the fact that I thought Jimmy was the killer). Near the end I found it easy to believe he wanted to enjoy the pleasure of making him suffer.

Christopher Gorham answered in a recent interview (check links section) Harper's Stars Delve Into the Mind of a Serial Killer: Henry Was "Born Bad" july 15, 2009

Was that a hard kill for [Henry]?
I think there were three really difficult murders for Henry (...) Everyone else, I don't think was difficult. (...)I think he was saving Jimmy. Jimmy was the golden goose kill. He would've really loved to kill him slowly.
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Do you have different ideas why? Would you like to share?