Casey and Sandy Parsons, the adoptive parents of missing 15-year-old Erica Parsons, say police have accused them of murder — but they maintain their innocence and insist the teen is living with her grandmother, Nan. However, police say there is no Nan and that Erica’s biological grandmother died five years ago.

WATCH: Erica Parsons’ Adoptive Mother Describes What She Says Happened The Last Day She Saw Her

Dr. Phil enlists the help of FBI Special Agent and Polygraph examiner Jack Trimarco to administer polygraph exams on Casey and Sandy. Both agree to take the test.

In the video above, Jack describes what happened during Casey’s test.

The couple refused to come back to the show to hear the results of Sandy’s test. In the video below, hear the results of Sandy’s test.