Julie Schenecker, a 53-year-old former military intelligence officer and interrogator, is charged with two counts of first-degree murder. She faces life in prison if convicted.
Prosecutor Stephen Udagawa began his opening statement by painting Schenecker as a calculated killer who planned the murders of her children, 13-year-old Beau and 16-year-old Calyx.
"This is the worst thing that I've ever done," Schenecker told police, aware of her actions, Udagawa told the jury.
Udagawa said that in 2010, Schenecker’s relationship with her daughter began to deteriorate. She didn't handle it well and started drinking and taking prescription drugs to numb the pain, he said. During this time, Calyx became more disrespectful and would say mean things to her mother.
In January 2011 when her husband was deployed overseas, Schenecker sensed he wanted a divorce, according to prosecutors. It was after her husband left when Schenecker began hatching a plan to kill her children, the prosecution said.
Udagawa told the jury they will see a video that shows the mother seeming pleasant and happy when she drove to a gun store shortly before the killings and purchased a .38 revolver.
According to the prosecution, Schenecker was disappointed when she learned there was a three-day waiting period to pick up the gun. Five days later, she drove back to the store and picked up the murder weapon, Udagawa said.
It was the night of January 27 when Schenecker followed through with her plan, according to the prosecution. Beau was sitting in the front seat of his mother’s minivan on his way to soccer practice when Schenecker pulled a gun on him, firing one shot through the windshield. Udagawa said Beau told his mother he was going to punch her if she didn’t put the gun away. That’s when Schenecker pointed the gun at his head and fired the fatal shot.
After killing her son, prosecutors said Schenecker turned the car around, drove home, and parked her car in the garage before shooting her son again in the mouth -- his "sassy" mouth as she wrote in her journal, Udagawa said.
Schenecker then walked up the stairs where her daughter was working on her computer and shot the 16-year-old in the back of the head, Udagawa told the jury.
According to prosecutors, the details of what happened that fatal night were recounted by Schenecker herself in a journal which was discovered by police at the Tampa home.
“Calyx was so [expletive] yesterday. On Saturday she called me an evil soul,” Schenecker wrote in an entry, Udagawa told the jury.
“Beau has become sassy since you left. Copying Calyx’s attitude. It kills me know[ing] that he turned on me. He has to come along with us,” another journal entry allegedly read.
Defense attorney Jennifer Spradley began her opening statement by explaining to the jury how mental illness transformed Schenecker's life -- an illness so severe that it was difficult to treat.
In order to understand why a mother would shoot her children, Spradley told jurors they have to go back to the beginning.
Schenecker had a troubled childhood, Spradley said. At the age of 6 she was molested and testified against her abuser at trial.
Despite her childhood abuse, Schenecker went on to live a productive life as a working woman in the military.
After marrying her husband, Spradley said Schenecker’s mental illness began to take over. At one point, Schenecker was checked into the hospital for nine months due to severe depression, Spradley told jurors.
After Thanksgiving 2010, Schenecker came out of treatment. However, the defense said she refused to leave her bed and began having constant suicidal thoughts.
When her husband left on deployment in January 2011, Spradley said Schenecker became deeply hurt by her relationship with her daughter and was determined to commit suicide.
Near the end of her opening statement, Spradley painted Schenecker as loving mother who fell victim to severe mental illness.
According to the defense, Schenecker told police she told her daughter she loved her before shooting her. And after killing her son, Schenecker allegedly told detectives she tried to lift his body and put him in her bed where he slept the soundest.
"We are going to ask you to find Ms. Schenecker not guilty by reason of insanity,” Spradley said in her final words to jurors.
The Julie Schenecker murder trial picks back up Tuesday morning. Watch Nancy Grace on HLN for all latest details from inside the courtroom.