Rex Heuermann told his ex-wife, Asa Ellerup, while he was in jail that seven of the eight women he later admitted to killing died in the basement of the family’s home on Long Island, according to a teaser for a new episode of a documentary series. Ellerup said the episode is scheduled to air Thursday on NBC’s streaming service Peacock, and that in the conversation Heuermann described the basement killings as occurring while she was away.

In the teaser, Ellerup said she asked Heuermann how many of the women he was confessing to had been killed by him. She said he responded, “Eight,” and she later described that response as confirmation that the eight women he had admitted to killing were his only victims.

Ellerup said she told investigators and family through the documentary series that Heuermann did not use his first name with her in a way that made it easy to reconcile what he said with who he appeared to be. In the teaser, she said she intentionally avoided using her former husband’s first name herself “to ‘put a wall up’ between the two,” and that when he began speaking, it felt like “that’s the Rex I know,” before adding, “But I didn’t want to see that one. I wanted to see the one I needed to see.”

Ellerup is the subject of “The Gilgo Beach Killer: House of Secrets,” and the latest and last installment of the series follows the release of the first three episodes last June. A second documentary, “Killing Grounds: The Gilgo Beach Murders,” is also set to be released Wednesday on Amazon’s Prime Video.

Heuermann’s guilty plea and admissions ended the yearslong investigation into the Gilgo Beach killings, and the latest documentary installment arrives as details about the case continue to surface through family members’ accounts and new programming. MSI previously reported that Heuermann pleaded guilty and admitted killing all eight victims.

Ellerup’s attorney, Robert Macedonio, declined to discuss what other new details the Peacock documentary episode reveals. In an email, Macedonio said the process has been “extremely emotional and painful” for the family and that Ellerup would like the focus to remain “on the victims and their families, who have suffered immeasurable and lasting losses.”

A lawyer for Heuermann’s two grown children, Victoria and Chris, said in a statement that the children “echo the sentiments of their mother” and “wish only to move forward as best they can” given “this remarkably dark chapter in their lives.” Heuermann’s lawyers did not respond to an email seeking comment.