Ailsa Jackson will testify against Sgt. Michael Walker at his murder trial scheduled for next August

By Greg Hanlon
Updated December 11, 2015 05:30 PM
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Allen County Sheriff's Department

The mistress of a married U.S. Army medic pleaded guilty on Thursday to stabbing the medic’s wife to death with a kitchen knife as she slept and then waiting a half-hour to make sure she was dead, PEOPLE confirms.

Ailsa Jackson, 25, admitted in court to meeting Sgt. Michael Walker on an online dating site and to allegedly conspiring with him to kill his wife, Catherine Walker, U.S. Attorney Thomas Brady, who prosecuted the case, confirms to PEOPLE.

As part of her plea agreement, Jackson is expected to be sentenced to 30 to 33 years in prison and will testify against Walker at his trial scheduled for Aug. 30, 2016, Brady confirms. Walker has been charged with first-degree murder by way of aiding and abetting and conspiracy to commit murder. He has pleaded not guilty and is being held without bail in the Federal Detention Center in Honolulu until his trial, Brady says.

Jackson admitted in court that Walker told her that he couldn’t divorce his wife but that his “deepest desire” was to have her gone, Brady says.

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Last November, Jackson said that they met in the parking lot of the Aliamanu Military Reservation in Hawaii and devised a text messaging coding system to indicate how she would enter the Walker home, Brady confirms: If Walker texted “good,” Jackson would enter through the window. If he texted “bad,” she would use a key left near the back door.

After Walker texted “bad,” Jackson said using a key enter the house, grab a knife, and stab Catherine to death, Brady confirms. Jackson stayed in the house for a half-hour to make sure Catherine was dead, Brady confirms.

At the time of the murder, Jackson was living with her family on the military reservation because her father served in the army, Brady tells PEOPLE.