MISSION, Kansas—Becky Harper sobbed as she spoke to a Missouri dispatcher after stumbling across her expectant daughter in a pool of blood, her womb slashed open and the child she had been carrying missing. “It’s like she exploded or something,” Harper told the dispatcher on Dec. 16, 2004, during the desperate yet futile attempt to get help for her daughter, Bobbie Jo Stinnett, who had been eight months pregnant. Lisa Montgomery, who strangled Stinnett with a rope before performing a crude cesarean and fleeing with the baby, awaits execution Tuesday. If the lethal injection is carried out as scheduled at the Federal Correctional Complex in Terre Haute, Indiana, Montgomery would be the first woman executed by the federal government in about six decades. Montgomery drove about 170 miles from her Melvern, Kansas, farmhouse to the northwest Missouri town of Skidmore under the guise of adopting a rat terrier puppy from …