( CNN ) -- A mother 's plot to blame a stranger for killing her sons went awry when one of the boys survived and told police how Michelle Kehoe cut his throat , then moved on to his younger brother , an Iowa prosecutor said Thursday . Police found the 7-year-old covered in dried blood in the family van the morning of October 27 , 2008 , in a secluded area near a pond east of Littleton . Beside the van , his 2-year-old brother lay dead , his throat also slashed . `` She cut me , '' the boy said in a high-pitched voice in an audio recording that was played Thursday in Kehoe 's first-degree murder trial . Kehoe , of Coralville , Iowa , has pleaded not guilty to charges of first-degree murder , attempted murder and child endangerment causing serious injury . Before the trial , her lawyers filed a notice of intent to present an insanity defense , according to court records . Kehoe 's lawyers chose to reserve their opening arguments for the start of their case . Dressed in a blue and white striped blouse , Kehoe frowned as she listened to her son 's voice on the recording , occasionally bowing her head . The boy had locked himself in the van overnight after his mother slashed him and his younger brother the previous day and left them for dead , Assistant Iowa Attorney General Andrew Prosser said in his opening statement . Kehoe then walked to a nearby pond and attempted to kill herself by slashing her throat with the same weapon , a camouflage-handle Winchester hunting knife she bought the month before , Prosser said . When it became apparent she was not going to die , the prosecutor said , she staggered half a mile down the road to the nearest home and told a story she 'd concocted weeks before of how a stranger abducted the family , killed her sons and tried to kill her . But when authorities went searching for the stranger , they instead found her 7-year-old son in the car and his younger brother dead outside the driver 's side . `` Do you know where you 're injured at ? '' Deputy Stephen Peterson asked the boy in the recording . `` Just my throat , '' the boy said . `` Who did that to you ? '' `` My mom . '' The boy said his mother also put duct tape over his eyes , nose and mouth , but that he pulled them off after his mother left him . `` She was hurting my baby brother , '' he said . Kehoe began plotting the attack the month before with the purchase of the knife and the duct tape , Prosser said . She allegedly chose the date of the incident to coincide with when her husband , Gene , was scheduled to take a yoga class , telling him they were going to visit her mother at a nursing home in Sumner . Police also say they found signs of a cover-up at the scene , including pieces of a first-aid kit scattered around the scene and a handwritten note documenting the attack , Prosser said . The note detailed how a man broke into the car when the family stopped at a gas station and forced them to the area where the van was found . Kehoe tried to fight him off with pepper spray but he knocked her unconscious , the note said , according to the prosecutor . Police said Kehoe later told them she had written the note in the midst of the attack to explain what had happened to those who would find the scene , according to the prosecutor . `` And the note , which you 'll see , ends with , 'Oh no , here he comes again ... ' `` Prosser told the jury . Kehoe faces life in prison without parole if convicted of first-degree murder for her son 's death .
Michelle Kehoe slashed sons ' throats , left them for dead , tried to kill herself , prosecutor says . Iowa jury hears tape of surviving boy telling police his mother cut him , hurt brother . Prosecutors say Kehoe hatched plan month before to blame attacks on stranger . Score: 7