Paranormal investigators featured on the Travel Channel's reality TV show "Ghost Adventures" died following a hostage standoff with police in Sparks, Nevada on Thursday.

The Reno Gazette-Journal reports that "Ghost Adventures" stars Mark Constantino and his co-star wife Debby Constantino were both found dead inside their daughter's apartment following a standoff with police.

The incident began on Tuesday when police received a call from a woman in neighboring Reno, Nevada who discovered her male roommate dead, Reno Police Lt. William Rulla told the Reno Gazette-Journal. The name of the victim has not been released.

As police investigated, they learned that the woman's other roommate, Debby Constantino, was missing.

Police located Debby inside her daughter's apartment in Sparks on Thursday by using a cellphone tracking device. Also in the apartment was her estranged husband Mark, who had kidnapped her.

The Sparks Police Department told NBC News that SWAT teams were deployed to the apartment. Neighbors were evacuated, and the surrounding area was locked down.

When officers knocked on the apartment door, several shots were fired, Reno Police Department's deputy chief Tom Robinson told NBC News station KRNV. Shots were also fired at police through the door.

A man told police through the apartment door, "Give me 15 minutes to gather my thoughts or I'll kill her," Robinson said.

Police negotiators and local FBI agents tried to persuade Mark to surrender. After three hours of negotiation, a SWAT team entered the apartment by using explosives to blast the door open. Inside, the "Ghost Adventures" stars were both discovered dead.

Police have not revealed the manner in which the couple were killed.

Officials have said the Constantino case and Reno shooting death appear to be related. The investigation is ongoing. No arrests in the shooting death have been made.

This was not the paranormal investigators' first domestic violence incident. Last month, Mark was charged with kidnapping and domestic battery against Debby. Their daughter, who lives in the apartment where the couple died, was charged as an accomplice in that incident.

Following that incident, Debby had obtained a restraining order against Mark.