I'm intrigued. I thought of Escape from New York. :)
I wondered why you needed a serial killer to do this job? He has the victim's memories, but his other skills seem to be: killing. Wouldn't you be better off using an FBI profiler or an ex-cop or a private eye? Someone skilled in tracking killers. That might also address the first comment, above, about deserving what's coming to him.
I know Escape from New York used the idea of 'you get a pardon' AND 'you get to live once we neutralise this deadly thing we've implanted in your neck' -- and it worked. But I did wonder whether the threat of death itself was enough. Like: 'find the killer and we'll let you live' doesn't need to also come with a pardon. Which makes it even easier to use one of the jobs I listed in the paragraph above. Just a thought!