NEW YORK (AP) — The man who recently pleaded guilty to New York’s Gilgo Beach serial murders told his ex-wife while in jail that he killed most of his female victims in the basement of the family’s dilapidated home, the latest episode of an NBC documentary series shows.

His ex-wife, Asa Ellerup, said in a teaser for the episode airing Thursday that Rex Heuermann also told her that the eight women he has admitted to killing were his only victims.

Ellerup says later in the teaser that he told her that he killed seven of them in the basement of the family’s house in Massapequa Park on Long Island while she was away.

“I said to him, ‘So Mr. Heuermann, I understand that you are confessing to me on these murders. Can you please tell me how many of these women did you kill’?,” she said in the 90-second clip. “He said, ‘Eight’.”

Ellerup said she intentionally didn’t use her former husband’s first name as a way to “put a wall up” between the two.