Both conversations were recorded in what police dubbed "Operation Puyallup", named after the city in Washington state where Steven Powell and his son were living.
The attempt to get the two to self incriminate didn't work. Josh Powell refused to discuss the disappearance, citing advice from his attorney, court documents say, and Steven Powell called Graves a "bitch" before ordering her out of his house.
Graves, who lives in Utah, told The Tribune on Tuesday that she suggested to police she be wired because she wanted to help find out what had happened to Susan Powell.
"In that situation, you feel so powerless," Graves said Tuesday of the search for Susan Powell.
Graves said she "absolutely" believes that Josh Powell killed Susan Powell and that her father and another brother, Michael Powell, also were involved somehow, possibly after the fact.
"By the evidence, it looks like Michael helped him (Josh Powell) hide the body," she said.
Graves said she and Michael Powell had been close as children and it was devastating to learn of his possible involvement.
As for Steven Powell, Graves said, "I still think he had something to do with it, even though they don't have any hard evidence."
Susan Powell was last seen on Dec. 6, 2009, at her West Valley City home, which she shared with her husband, the only person of interest ever named in the case.
Josh Powell claimed he left his wife at home as he took his sons, Charlie and Braden, then ages 4 and 2, on a late-night winter camping trip in the West Desert of Utah. He denied having anything to do with the disappearance.
On Monday, West Valley City police closed the active investigation into the disappearance and released thousands of pages of document related to the case.
Graves went to her father's house in Washington with her husband after police obtained a court order allowing the recording. She doesn't think her father and brother suspected she was wearing a wire but couldn't be sure.
"I was very scared," she said. "I had no idea what they would do if they figured it out."
Court documents say Graves told her brother that she had heard rumors that he would be going to jail for a long time and suggested that he take a plea bargain. Josh Powell said he hadn't done anything but Graves continued to press him about his actions on the night his wife was last seen by anyone outside the family.
"I didn't have anything to do with it," Josh Powell said of the disappearance, according to records.
Graves said she has written a book about her perspective on the case and her nephews' deaths at the hands of their father. The self-published book, "A Light in Dark Places," is slated for release in June and will be sold through Amazon, she said.
She has mixed feelings about the active investigation being closed, saying she's a little disappointed but also ready to move forward.
"I know where she is," Graves said of Susan Powell. "She's up in heaven with Charlie and Braden."