If it went down as he described to the police, there was probably enough incriminating physical evidence that lawyering up would have been a less than optimal option. It's likely it would not have taken Dexter to impeach his story.
After what he did, the only rational option would have been to have disposed of the bodies and gone on as if nothing unusual had happened. And hope that the kids hadn't told any of their friends they were planning to rob that old codger in the big house at the end of Elm Street. Because if they had, you can bet the cops would have come knocking with a warrant, substantially raising the clean-up standard.
But this old coot was hardly rational, having apparently been driven over the edge by previous break-ins.