A Florida jury must decide whether a former Army linguist knew what she was doing when she killed her two teenagers — by shooting each in the head and mouth — or whether she was insane at the time and couldn't tell right from wrong.

Prosecutor Jay Pruner terrytold jurors at the conclusion of Julie Schenecker's trial on first-degree murder charges that she methodically planned and carried out the killings because she was afraid that her husband was about to divorce her.

But defense attorneys said a heavily medicated Schenecker suffered from such severe depression and bipolar disorder that she could not tell right from wrong when she pulled the trigger. They urged the jury to find her not guilty by reason of insanity.

If convicted of first-degree murder, Schenecker faces a mandatory life sentence; Prosecutors are not seeking the death penalty. If acquitted by reason of insanity, she would be committed to a mental hospital until doctors and a judge agree that she is no longer a danger to herself or others.

Pruner said in closing arguments that Schenecker was sane when she fatally shot her 16-year-old daughter Calyx and her 13-year-old son Beau in January 2011 while her now ex-husband, Col. Parker Schenecker, was on a 10-day deployment to the Middle East. The prosecutor said she knew what she was doing and planned ahead of time.

"Focus on the state of mind of the defendant at the time of the offense. That is the critical time frame," he said.

Pruner told the jury that Schenecker was "desperate, depressed, angry, but very determined." He said she was despondent over what she thought was the inevitability of divorce.

"These were deliberate, well planned, well implemented and well concealed homicides," Pruner said.

He showed the jury photos of the children's bodies and magnified copies of Schenecker's journal entries before and after the shootings.

"I offed Beau," one entry said.

"I was planning on a Saturday massacre," she wrote in another entry, explaining how she bought a gun but had to wait three days for a background check.

Defense attorney Jennifer Spradley asked jurors to consider Schenecker's state of mind when she pulled the trigger. She was suffering from such severe depression and bipolar disorder and taking such "an extreme cocktail of medications" that she didn't understand what she was doing.

"Her mind is clouded. She didn't choose this illness — it chose her," Spradley said. "When she wasn't sick, she was a good mother."

She said that the family's frequent moves because of Parker Schenecker's military career exacerbated her illness and forced her to try new doctors and new treatments, including a nine-month hospitalization.

Trying to show the Schenecker loved her children, she quoted from a 2008 letter she wrote Calyx.

"I can never thank you enough for coming into my life. I love you dearly. I hope that you will love and accept me with all my imperfections."

All six mental health experts who testified during the trial said Schenecker was mentally ill, but the three called by prosecutors said she was legally sane when she shot her children.

Testimony showed that Schenecker bought a .38-caliber handgun the weekend before the shooting, telling the gun store clerk she wanted it for home protection. But in her journal, she lamented the three-day wait for a background check, writing she had planned a weekend massacre. When she collected the gun, she bought more lethal hollow-point bullets.

A few days later on the way to soccer practice in the family minivan, she shot Beau twice, investigators found — once in the side of the head and once in his mouth.

She turned around, drove home and parked in the garage. Schenecker approached Calyx from behind and shot her once in the head and once in the mouth.

Schenecker wrote about the shootings in her journals, saying that she shot both teens in "their mouthy mouths."

She also put a sticky note on the calendar that said, "Beau is in the van on the way to practice. Calyx is in her bed, tried to make her comfortable."

In her journal, Schenecker addressed her husband, writing that he was lucky he wasn't in the house, prosecutors said. "I might have taken you out, too," she wrote.

Schenecker told detectives after her arrest, "This is the worst thing I've ever done."

Schenecker also wrote that she wanted to kill herself and wanted to be cremated with her children, their ashes mixed together. She mentioned that she was going to try to move her son's body into her bed and wanted to die next to him.

"Beau and I are going to heaven," she wrote. "Wish heaven for Calyx too."