Prosecutors in Idaho plan to pursue murder charges against a doomsday couple accused of covering up the deaths of two children. In a previously undisclosed recording played in a hearing for Lori Vallow and Chad Daybell Wednesday, Prosecutor Rob Wood told Vallow’s sister that he was “going to be filing conspiracy to murder charges for both Chad and Lori”—charges that could potentially result in the death penalty. Defense attorneys for the pair are now fighting to get Wood taken off the case, claiming the tape is evidence of prosecutorial misconduct.

The case began after relatives reported Vallow’s two children missing last November; their remains were found buried on her partner’s property in June. The couple has so far been charged with various crimes relating to the concealment of evidence but has not been charged with murder. They did not appear at the hearing Wednesday.