Just when the story of Robert A. Durst, the New York real estate scion who is a suspect in two murders, could not get any stranger, a new book arrives from a former Westchester County district attorney, Jeanine Pirro, describing her quest for justice in his case.

As she frequently reminds readers of “He Killed Them All,” Ms. Pirro donned custom-made armor — Armani suit, Chanel bag and Manolo Blahnik pumps — to pursue an investigation from 1999 to 2005 into the mysterious disappearance of Mr. Durst’s first wife, Kathleen.

But details in her 313-page account, which was published on Tuesday, are already being challenged by some of her former investigators; friends and relatives of Kathleen Durst; the Durst family; and the original co-author of the book, who was fired in June.

Ms. Pirro’s critics fear that her memoir could aid Mr. Durst’s defense and provide a major headache for prosecutors in Los Angeles, where Mr. Durst is accused of murdering a onetime confidante to prevent her from disclosing what she knew about how Mrs. Durst vanished in 1982.