Out of his suffering, Caleb Carr learned to despise violence, fear insanity and probe the origins of cruelty. In his best-known book, “The Alienist,” John Schuyler Moore is a New York Times police reporter in 1890s Manhattan who helps investigative a series of vicious murders of adolescent boys. Carr would call the novel as much a “whydunit” as “whodunit,” and wove in references to the emerging 19th century discipline of psychology as Moore and his friend Dr. Laszlo Kreizler track down not just the killer’s identity, but what drove him to his crimes.

“The Alienist,” published in 1994 and the kind of carefully researched, old-fashioned page-turner the Beats had rebelled against, combined fictional characters such as Moore with historical figures ranging from financial tycoon J. P. Morgan to restaurateur Charlie Delmonico. Carr also featured the city’s police commissioner at the time, Theodore Roosevelt, with whom the author felt a surprising kinship.

“Personally and psychologically, I had always found TR one of the most compelling figures in U.S. history,” Carr told Strand Magazine in 2018.

“Later I realized that some of this had to do with the fact that, as a young man stricken by physical ailments and the fears they inspire, he was brought through his darkest times by his father, a deeply compassionate and caring man. This is often key to great men with noble hearts: an overtly caring father. Having had the reverse — a father who was the chief cause of my childhood fears and ailments — I was drawn to what was, for me, an exotic upbringing.”

“The Alienist” sold millions of copies, inspired the bestselling sequel “Angel of Darkness” and was adapted into a TNT miniseries that starred Daniel Brühl, Luke Evans and Dakota Fanning. Carr was so successful a novelist that his background as a military historian became obscured, or even trivialized. He taught military history at Bard College, was a contributing editor to the Quarterly Journal of Military History and had a close relationship with the scholar James Chace, with whom he wrote “America Invulnerable: The Quest for Absolute Security from 1812 to Star Wars.”

Carr had written for years about possible terrorism against the U.S. and published a book-length study a few months after the Sept. 11, 2001, attacks. In “The Lessons of Terror,” he contended that military campaigns against civilian populations inevitably failed and drew upon lessons dating back to ancient Rome. “The Lessons of Terror” sold well, but some critics thought he was not up to the job.

New York Times critic Michiko Kakutani wrote that Carr “has little credibility as military historian or political analyst,” and suggested he stick to thrillers, while Salon’s Laura Miller called some of his contentions “slippery and elusive as a handful of live minnows.” Enraged, Carr answered with an all-caps letter to the editor of Salon, in which he suggested that Miller and Kakutani should lay off military history and instead “chatter about bad women’s fiction.”

“Several reviews have made claims concerning my credibility that are, quite simply, libelous, and will be dealt with soon,” he later posted on Amazon.com, on which he gave his book a 5-star rating.