I agree with @Steven Stokes & @David T. 's advice. My experience with dealing with a slumlord also backs up the notion that that don't give a hoot about code violations. If they did, they would fix them.
There are a lot of examples in the forums on contacting owners about purchasing their property. Format a nice letter, leave the code violations and communications out of it, and maybe something will come of it. But,expecting to buy it for $20k--unless he's not been following real estate prices for many decades, that would seem to be unlikely.
Use this letter as a jumping off point for a larger letter writing campaign and you might snag a deal through the quantity approach. This could be a great jumping off point for this type of deal, whether its this one or another down the road. Here's a forum thread I started earlier this year that has some basic ideas to ponder:
What to say when contacting an absentee landlord