She has spent 15 years on Durst's trail, making him wary of her and giving her a unique perch from which to comment on Durst's latest arrest for the Fox News Channel, where she's the host of "Justice with Judge Jeanine."
She doesn't pretend to be objective. In an interview with The Associated Press, she said, "Every ounce of my prosecutorial being says this guy is an evil person."
She insists he was responsible for the death of his first wife, though he's never been charged; should not have been acquitted in the killing and dismemberment of a Texas neighbor; and was behind the killing of his friend in California.
In 2000, Pirro, then the district attorney in Westchester County, New York, reopened the cold case of the 1982 disappearance of Durst's first wife, Kathie. Durst was never charged, but Pirro refused to rule him out as a suspect. The case has since been declared a homicide.
Pirro told The AP she was driven to solve the killing partly because of a connection she felt with Kathie Durst.
"She was in med school not long after I was in law school," Pirro said. "There really weren't a lot of women in professional schools in those days. We were both trying to make it in a man's world."
As part of the reopened investigation, Pirro said, she planned to question Susan Berman, who was Durst's confidante and spokeswoman at the time of Kathie Durst's disappearance.
On Christmas Eve 2000, Berman was shot to death in her home.
"The first person I thought of was Robert Durst," Pirro said. Durst was charged last month with Berman's murder.
In 2003, when Durst went on trial for another killing — his admitted shooting and dismemberment of a neighbor, Morris Black — Pirro made several appearances in the courtroom in Galveston, Texas. Durst claimed self-defense, arguing he cut up the body in a panic and fled because he knew Pirro was looking into his wife's death and no one would believe him. That was also why he sometimes posed as a woman, his lawyer said.
The judge included Pirro in a gag order, and Durst's lawyer said in closing arguments, "If Ms. Pirro kept her mouth shut, none of this would have happened."
Durst's acquittal astonished Pirro.
"I believe that jury in Galveston got that just plain wrong," she said.
Pirro, a popular Republican in an increasingly Democratic county, won three terms as district attorney. But her political career was probably stunted by her husband, attorney Albert Pirro, who acknowledged he fathered a child with another woman and was convicted in 2000 of tax evasion and conspiracy after an embarrassing trial that laid out the couple's lavish lifestyle. She won a third term as district attorney while he was imprisoned.
After leaving office in 2005, Jeanine Pirro announced she would challenge Clinton for a U.S. Senate seat. In declaring her candidacy, however, Pirro misplaced a page of her speech and went silent for 32 seconds. The campaign did not recover and she gave up after two months, running instead for state attorney general. She lost to current Gov. Andrew Cuomo.
In 2006, Pirro tearfully announced she was being investigated by federal agents over a plan — which she said she never implemented — to secretly record her husband, whom she suspected of having an affair. She was never charged.
The Pirros divorced in 2013. They have two grown children.
When Pirro, 63, attended Durst's bail hearing in New Orleans last week, defense attorney Dick DeGuerin told the judge that Pirro was a potential witness, and on Wednesday, the defense asked the judge to subpoena her. DeGuerin said he thinks "she's being untruthful" when she says she planned to interview Berman before she was killed.
Ellen Strauss, a longtime friend of Kathie Durst, said Thursday that she had tried but failed to get Pirro to see Berman and that Pirro is engaging in "historical revisionism" on the subject of Berman. Pirro issued a statement saying, "This is about establishing the guilt of Robert Durst. Any collateral issues serve only to cloud that fact."
Pirro said she thinks Durst cooperated with "The Jinx," which seemed to uncover new evidence against him, because, "It's all about Robert Durst wanting attention. I think he's a devil and he likes to dance on the edge of a cliff and say, 'Look at me, look at me,' and his money has always gotten him out of things."
She said that when she saw Durst shackled in the New Orleans courtroom, "I said to myself, 'This is where he deserves to be and this is how he deserves to be treated.'"