Jurors in her capital murder trial also were told Saturday by Deputy Michael Stephens that he heard Yates tell the interviewer she didn't have to kill all five children, that the baby, six-month-old Mary, alone would have quote "justified all of them."
If there has been a bombshell in this case, this is probably it, says CBS News legal consultant Andrew Cohen. To the extent that the testimony describes Yates' state of mind last June 20th, that's "dynamite in this case," Cohen says, and the defense is going to have to quickly repair the damage during cross-examination if that's possible.
Yates has pleaded innocent by reason of insanity. Part of meeting that definition under Texas law is proving someone didn't know right from wrong while committing a crime, Cohen explains.
Earlier, a medical expert testified Yates was determined, decisive and exhibited an element of deception when she drowned her children.
"Each of these children did not want to die and they fought their deaths," said Dr. Harry Wilson, a pediatric pathologist from Texas Tech University School of Medicine.
But Cohen reports Wilson had to backtrack a bit on cross examination after he revealed that he hadn't reviewed Yates' mental health records.
Wilson described bruises on each of the children's bodies and used a life-sized infant doll to show how Yates, 37, pushed the forehead of her youngest child, 6-month-old Mary, against the bottom of the bath tub.
Wilson, testifying for the prosecution, said it would take at least three minutes under water for each of the children to lose consciousness, and another three for them to actually die.
After she removed each child from the water, Yates had time to resuscitate them, but didn't, Wilson said.
Tears rolled down Yates' face Saturday as she listened to Wilson describe her children's struggles for life.
On Friday, forensic psychiatrist Dr. Park Dietz testified for prosecutors that Yates allowed earlier opportunities to kill her children pass because she "wasn't ready" and had to get mentally prepared.
When Yates was asked during a Nov. 7 videotaped interview with Dietz how she got ready, Yates replied: "Just mentally, to do it."
"I needed to go ahead and do it," Yates said of her decision to go ahead with the drownings of her five children June 20 after her husband had left for work.
During the interview, Yates becomes misty-eyed but kept her composure as she detailed for Dietz how she killed the children, four boys and a girl.
Dietz, who was to undergo cross-examination Saturday, has worked on other high profile cases including that of serial killer Jeffrey Dahmer, "Unabomber" Ted Kaczynski and South Carolina child killer Susan Smith.
Dietz concluded from his review of police statements, Yates' medical records, court documents and interviews with her and others who know her that despite a severe mental disease, she knew her actions were wrong.
And that, says consultant Cohen, may be enough in itself to convict Yates.
Dietz said that to a "reasonable degree of medical certainty" Yates knew right from wrong that day, and that alone ought to be enough to carry the day for the State if, and it's a big if, jurors think Dietz is right and the defense experts all were wrong, Cohen explains.
Why is what Dietz said enough to convict? Because the "knowledge or wrongfulness" question is really the only one left unanswered as the case winds down, says Cohen. The other material element of Texas' insanity statute-whether the defendant had a "mental disease or defect" at the time of the killings-already has been conceded by prosecutors and by Dietz himself.
Dietz wouldn't say if Yates met Texas' legal insanity definition, but did say he believed she knew her actions were wrong in the eyes of the law, society and God.
Defense attorneys are trying to prove Yates, who has been diagnosed with schizophrenia by both defense and prosecution experts, thought in her delusional, psychotic mind that drowning her children was the right thing to do and the only way to save them from eternal damnation.
Yates faces two capital murder charges for the deaths of Noah, John and Mary. She could later face charges for drowning Paul and Luke. If convicted, she could be sentenced to life in prison or the death penalty.
The case could go to the jury next week.