She has written books on child abuse. Several years ago, the Army called on her to help it address alarmingly high rates of child abuse among military families.

This month, she's a pediatrician that a Johnston County jury must trust enough to believe that Lynn Paddock murdered her 4-year-old adopted son, Sean, through calculated, sadistic torture.

Cooper stepped into the witness box Thursday morning, comfortable and assured. She was the last witness for the state in its case against Paddock.

Cooper follows Paddocks' other children, who testified about lashings with plastic plumbing supply line, mouths sealed shut with duct tape and orders to eat feces and vomit. Cooper examined all of the children over the past year, taking notes about their insomnia, stunted academic performance and suicidal thoughts.

Her job is to explain to jurors what all this means, and much rests on her. Typically, a jury must find that a defendant premeditated a killing to be guilty of murder in the first degree. Prosecutors are not saying that Paddock calculated Sean's death. Instead, they have suggested that they'll ask the jury to find her guilty of first-degree murder through a more unusual legal theory: murder by torture.

Cooper stood beside a flip chart Thursday afternoon, a few feet from the jury of strangers who will decide Paddock's fate. The doctor scribbled notes about the methods that distinguish ritualistic abuse from torture. Binding a child at night and stealing the essential human function of sleep is torture, she testified. Paddock's orders to her children to drink quarts and quarts of water, then sit in their urine-soaked underwear, Cooper testified, was sadistic child abuse.

"They're set up," Cooper said. "They can't escape. They'll get beaten regardless."

Paddock's lawyers had tried to block Cooper from testifying. They've complained to a judge that she didn't turn over any of the medical studies or textbooks she used to form her opinions.

Cooper and prosecutors say her conclusions come from a career of exposure to abused children and from a library of pertinent literature. Reading her resume in court Thursday took nearly 15 minutes.

Paddock's lawyers persuaded a judge Thursday to prevent Cooper from telling jurors her opinion that Lynn Paddock adopted foster children to collect money. The state paid Paddock and her husband more than $2,000 a month to rear their six adopted children.

On Thursday, Paddock's attorneys rose to object to Cooper's testimony many times. Twice, they asked the judge to declare a mistrial, saying Cooper testified about things she had never mentioned in her reports. They also argued that Cooper was trying to profile Paddock as a particular kind of child abuser, a tactic that they argued is not allowed.

Today, Paddock's lawyers will get their chance to grill Cooper. Then, the state plans to rest its case and turn over the witness box to Paddock's attorneys.