According to Zillow, the last sale of the house was in 1979 for $68,000. PG was in prison from 77-88, but I have a hunch his parents bought the house and he and NG moved into it and manipulated themselves into holding the title.
A 3 BR, 1 BA home on a 12,000+ square foot lot in Antioch appreciated in value over the years, all the way up to around $460,000 in early 2006, which is when this area started seeing the real estate decline.
I'm not defending this freak (the comment about computer & his being a SO), just trying to explain that this snake most likely re-financed the property. Like a lot of homeowners around here, he could have done it every few years as values increased, pulling out cash equity every time. We noticed the house appears to have a fairly new roof on it, he probably justified one or two re-fi's for home improvement purposes, and who knows what else.
http://www.zillow.com/homedetails/1554-Walnut-Ave-Antioch-CA-94509/18295462_zpid/