agreed, start him off in the job. as far as him reminescing (sp), i'd keep that to a minimum as apparently you're thinking of a series here and will likely want to use part of his past for current events. if you lay all the past out, it'd be harder to refer back to if you need the details to be different.
personally, i wouldn't consider a 'prequel' for a series as i'd want to reserve the past to be meted out during the regular novels when you need it. like i said, i wouldn't want to be locked into something if i didn't know what the future had in store. once several are done and the character is a success, then maybe you can cull together all those pieces of the past for a new adventure in a 'prequel' fashion. i don't like the idea as his backstory used as a first sequel, though i can certainly understand the temptation.
were it a series i had in mind (bear in mind i don't tend to think in terms of series), i'd probably have a few details about his past defined for that particular story, then, thinking ahead of doing a backstory novel, i'd add some vague details in there. for example, a college girlfriend whose name is mentioned often enough and seems to dredge up some amount of angst, yet whose fate is never defined. i would even take it a step further and perhaps have the MC have to deal with her father, a DA or recruiter for the texas rangers (who always snuffs his chances at joining), and have the two have a lot of anger and aninimity (sp ~ sorry, it's early) towards. in other words, have a broad backstory in mind, but don't establish it so much that it hinders the current stories; but, at the same time, hint at certain past events so that you can have a solid 'prequel' that ties the series together nicely.
how would i do it? i'd write about seven highly successful novels (because i rule), do a 'prequel' (maybe incorporating the backstory into a current mystery, not sure), then reveal that jenny isn't dead after all, but the MC had made a terrible, terrible mistake he can't shake. jenny moved on, porked out a couple of brats, and claims to be happy with her jerk-off husband who probably is in a spot of trouble, thus re-uniting the lost lovers. and then i'd have enough fodder for another series as the MC attempts to redeem himself in her eyes. the 'prequel' would serve as just a kick-off to more books. hm, i'm thinking the MC made such a bad decision that it cost his g/f her sister's life. yeah, i like that ~ it also gives the MC a lot of motivation for his life of kicking bad guys' asses the way he does and why he utterly freezes up in hostage situations... or something. probably pretty cliche, lol.
but, yeah, the lonely cop with a mysterious past is pretty standard fare, imo (at least in movies: i assume it's pretty standard in fiction, too). but, it's also something that gets published time and time again (i forget the one i'd read, but the woman's name was 'winter,' which i thought was pretty lame).
anyhoo, i'd start off with him already settled. good luck.
