HOUSTON, Texas (CNN) — Closing arguments began Tuesday morning in the trial of a Texas woman who claims she was legally insane when she drowned her five children last year.

The closing arguments will wrap up three weeks of testimony from police, medical experts and family members. Prosecutor Joseph Owmby quickly made his arguments, and defense attorney Wendell Odom followed.

The defense rested Monday after calling rebuttal witnesses in the trial of Andrea Yates. The prosecution rested over the weekend.

Defense attorneys introduced more psychiatric testimony Monday in an attempt to show that Yates did not know right from wrong at the time she killed her five children June 20, 2001.

Under Texas law, if jurors believe 37-year-old Houston woman knew right from wrong as she drowned her children one after another in the family bathtub, they cannot find her legally insane.

If Yates is acquitted, the court will have to wait at least 30 days before deciding whether she should be committed to a mental hospital or go free.

Yates is being tried on two counts of capital murder, one covering the deaths of Noah, 7, and John, 5, and the other covering the death of Mary, 6 months. She is not on trial for the drownings of Luke, 3, and Paul, 2.

The two capital murder charges are based on provisions in Texas statutes. One charge covers the intentional deaths of two people in the same event or scheme; the other covers the death of a child under 6.

Jurors will have to decide whether Yates knew her actions were wrong as she drowned her five children in the family bathtub last summer. Neither the state nor the defense contests that Yates suffered from a severe mental disease or that she killed her five children on June 20 of last year.

The defense argues that the mother of five was insane, while the prosecution contends Yates knew killing her children was wrong and that the acts were premeditated.

To prove insanity, her attorneys must show by a greater weight of evidence that Yates was too mentally deranged to know her actions were wrong. In Texas, a person is presumed sane.

The issue of Yates' ability to differentiate right from wrong is crucial to the capital murder case. Under Texas law, if jurors believe Yates could tell the difference, they cannot find her legally insane.

Stephens testified he heard Yates tell the psychiatrist, "'I knew what I did was wrong.'" In testimony over the weekend, a sheriff's deputy said he heard Andrea Yates tell a jail psychiatrist that she knew she was wrong when she drowned her five children last June.

According to the deputy, Yates told the doctor, "'I didn't mean to hurt them. I'm so stupid. I'm such a monster.'"

Deputy Michael Stephens of the Harris County Sheriff's Department testified Saturday he overheard Dr. Melissa Ferguson's conversation with Yates on June 21, 2001, one day after the killings.

Ferguson testified for the defense earlier in the trial that Yates was "one of the sickest patients" she had ever seen and exhibited extreme signs of paranoia and delusions. Yates could not have known right from wrong, Ferguson testified.

Defense lawyers questioned the deputy's testimony from the outset, challenging his accuracy and motive because he did not write down his recollections until after he was contacted by prosecutors on February 13.

Defense attorneys grilled Stephens about the eight-month lapse between the interview and the five pages of notes he wrote earlier this month. They also challenged Stephens about his testimony regarding Yates' comments about her husband, Russell Yates.

According to Stephens, Yates told Ferguson that she killed Mary because "'Russell didn't want another girl. He wanted another boy, for a basketball team.'"

— CNN Correspondent Ed Lavandera contributed to this report.