see the problem I might have with a prequel is you have the destination already... So the character progression and I am speaking out my ass here, but the progression would feel very direct route.
If somehow you can use the before to support a future character change then maybe you have more complexity allowing you to write them in tandem.
When we join back with him in the now then we also have gained something valuable because we already have an attachment with this event hence an attachment to anything before it and that will support how I would feel about any new predicaments and even have input as to what I wish he would do based on previous events. All nice and fresh in my memory.
Yip Shanderlock sounds great. :)
Hmm, now that you've mentioned it... And describing the tedious police work he was doing before he ended in there would've been boring anyway... Maybe. ;)
It's definitely a character I want to write more on - like the killer chemist from "A revolutionary product". I think they're two characters that are unpredictable both for me and for the reader, which is exactly why they can be (and are) so awesome.
Definitely worth a revisit. If not in the same setting, at least with the same or similar character. ^^
Maybe the chemist could be called Shanderlock. Nice and mysterious.