Candace Aikin testified at a hearing on what hearsay testimony, if any, prosecutors can use at Peterson's trial on charges of killing his third wife, Kathleen Savio, the Chicago Sun-Times reported.
"He said he could kill and make it look like an accident," Aikin said.
Aikin's niece, Stacy Peterson, quickly answered, "Not with this chick, you don't," Aikin added, crying as she spoke.
Aikin testified Stacy was so desperate to get out of her marriage she said she wished her husband would hit her.
Also Tuesday, Will County Judge Stephen White ruled a minister who counseled the couple can testify about statements Stacy Peterson made to him. White said he expects to decide Wednesday whether Neil Schori can also testify about Stacy's statements quoting her husband, the Chicago Tribune reported. Defense lawyers argue those statements are covered by marital privilege.
Peterson, a former police officer in Bolingbrook, Ill., is charged only with killing Savio, who drowned in a bathtub. Prosecutors have said they hope to link him to the disappearance of Stacy Peterson.
The public and news media were barred when Schori testified at the hearing.
White has said Schori cannot testify about his counseling sessions with the Petersons in their home or with Drew alone but Schori, a non-denominational minister, can tell a jury about sessions with Stacy in public places.