Ok, so it doesn’t say a thing about the plumber.
Sure isn’t a very illuminating article. Since the perv apparently had his victims concealed behind an extremely heavy door, there’s no reason to think an occasional escorted visit to the basement by a repairman is evidence of an accomplice. I can’t imagine any house going 24 years without requiring some type of professional work on utilities in the cellar — drain pipes, furnace, etc.
The wife, however, is either severely mentally deficient, or was a willing enabler of this horror. Missing daughter, children appearing out of nowhere, and a husband who prohibited her from entering the cellar in her own house, yet spent entire nights down there himself ???