The former wife of Arthur Allan Thomas has written to Justice Minister Simon Power asking him to reopen the case of the 1970 Crewe murders.
Mr Thomas was twice convicted of killing Jeanette and Harvey Crewe at their Waikato farm before being pardoned in 1979.
A Royal Commission in 1980 found the police had planted evidence. No-one else has ever been charged over the deaths.
The Crewe's baby daughter was on her own for several days and a woman who was seen entering their farm in the days after their killing is believed to have fed her.
Mr Thomas' former wife Vivien Harrison has written to Justice Minister Simon Power asking him to do whatever it takes to identify the woman, because she says it was not her.
Mr Power's office says the minister is considering the letter.
Investigative journalist Pat Booth, who campaigned for Mr Thomas's release, says he can understand Vivien Harrison's concern, as people thought she was the mystery woman, but she's been cleared along with her former husband.