Gilligan's attorney, Sandra Carr, tried to argue the mother, who was then 39, was a gold-digger taking advantage of a lonely and elderly man, claiming he bought her a home, car and motorcycle.
She also argued that nurses found no physical injuries or marks on the boy's wrists or ankles indicating he had been tied up, and questioned why the mother didn't use the computer or any other devices in the home to call for help.
Carr also claimed that the woman re-called police back to the home after an initial search, and that they found more evidence the second time, suggesting the mother had staged some of it.
Gilligan, who is a convicted murderer, will be sentenced on December 5.
In February of 1988, he was arrested and sentenced to life in prison for the slaying of his own stepfather eight years earlier. He was released from prison in October 2014.