The investigation into the deaths of a ghost-hunting couple in Nevada has determined a male roommate of the woman was fatally shot in the head in a Reno home several hours before police found the paranormal investigators in a barricaded apartment.

Debra and Mark Constantino had appeared on the Travel Channel's series, "Ghost Adventures," including episodes shot at the Mustang Ranch brothel near Reno. They were found dead Tuesday at their adult daughter's apartment across town in Sparks after a two-hour standoff that ended when a SWAT team burst through the door to find their bodies.

About seven hours earlier, Debra Constantino's roommate, James Anderson, was found dead in his Reno home, Sparks police Lt. Rocky Triplett said. That's when they determined Debra Constantino was missing and that she and her husband had a history of domestic violence and were in the process of getting divorced.

Click here to subscribe to FOX411’s YouTube channel

Officers encountered gunfire when they arrived at the apartment near Sparks High School at about 11 a.m. but didn't return fire, Triplett said.

Negotiators made contact with Mark Constantino almost immediately and last talked to him about 1:15 p.m., he said. A short time later they heard a single gunshot and the SWAT team rushed in.

The manner of death has yet to be determined pending the completion of the autopsies, Triplett said Friday.

Washoe District Court records show Debra Constantino obtained a restraining order that was served on her estranged husband last week, and the two were scheduled to appear in court in December regarding their pending divorce.

People who knew them gave mixed accounts of their relationship.

Janice Oberding said she became friends with the Constantinos while teaching a class on ghost hunting and spirituality at the Truckee Meadows Community College in 2012. She said she was shocked to learn of the killings.

"We drifted apart and our friendship ended," Oberding told the Reno Gazette-Journal. "But I know at one point she loved him very, very much and he loved her."

Rebecca Evans, 72, of Reno, said she worked as Debra Constantino's life coach and spiritual guide for three years. She said she didn't believe they had any domestic issues early on but problems later progressed.