A jury in Dallas on Thursday found 50-year-old Mark McCay guilty of attempted theft.
McCay faces up to 20 years in prison. A judge will sentence McCay next month.
Mary Ellen Bendtsen died in 2005. The trial involved her historic 7,000-square-foot Swiss Ave. mansion.
The Dallas Morning News reports prosecutors say McCay, who'd been friends with the woman for about 15 years, took advantage of her dementia. A will allegedly signed by Bendtsen after a stroke and less than two weeks before her death left her 1917 home to McCay and his partner.
McCay remains free on bond. Two co-defendants await trial.
Bendtsen's only child sold the house last year for $525,000.