Retired Trinity University economics professor William Breit relaxes in his home. He and co-author Kenneth Elzinga soon may begin their fourth murder mystery. Jerry Lara/Express-News

It's an approach favored by William Breit, retired Trinity University economics professor and co-author of a series of murder mysteries in which the sleuth is an economist.

"Crime is a business," Breit said. "It's a way for people to gain benefits. If you lower the cost for a given benefit, a prediction can be made that crime will increase."

Breit, along with co-author Kenneth Elzinga of the University of Virginia, has written three novels under the pseudonym Marshall Jevons. The two have stretched those efforts over 20 years and two time zones, between full-time teaching and Elzinga's work as an antitrust consultant around the Microsoft case.

Elzinga says he's coming to San Antonio soon with a folder full of ideas for a possible No. 4.

Their fictional hero is Henry Spearman, an impish, balding Harvard professor who never misses an opportunity to pontificate on the economics of everyday life. The novels find the protagonist, and his ever-patient wife, Pidge, unexpectedly surrounded by murder and intrigue.

Starting from the belief that most human actions are self-serving — that is, designed to maximize marginal utility (some might call it happiness) at the lowest cost — Spearman figures out who among the suspects has behaved in way that flies in the face of that notion, thus betraying guilt.

Part Lt. Columbo, part Milton Friedman, the often didactic Spearman lays out principles early in the books that later will reappear in a different form, holding the clue to the whodunnit.

The result has been warmly received. After the publication of the first book, "Murder at the Margin," the Wall Street Journal opined, "If there is a more painless way to learn economic principles, scientists must have recently discovered how to implant them in ice cream."

The writers' own role model concurs.

Milton Friedman, now in his 90s, was something of a household name during the latter part of the 20th century. Winner of the 1976 Nobel Memorial Prize in Economic Sciences, he served on Ronald Reagan's economic policy advisory board, where his libertarian advocacy for deregulation and small government was much appreciated.

"I don't deny paternity," Friedman said Monday by phone from his northern California home. Spearman is recognizable "mostly due to height and mode of reasoning.

"The analysis was correct in economic terms. It's deductive reasoning, looking for indirect effects, " he added. "Inferring what would maximize a criminal's utility, (you guess) what clues you should look for."

Economics isn't just about money or inflation, said Jorge Gonzalez, chairman of Trinity's economics department. "It's a way of thinking. That's what makes economics so powerful."

Breit is a San Antonio native and an alumnus of Jefferson High School and the University of Texas at Austin. He returned home in 1983 after 18 years teaching at the University of Virginia, where, with Elzinga, he frequently wrote on antitrust issues.

A scholarly article was turned into a book on the subject in 1976, asserting that white-collar crime was prevalent because the benefits outweighed the likely penalties.

That theory can be applied to any criminal behavior, a notion he bounced off Elzinga and his wife when the couple joined the bachelor Breit in a vacation to St. John, in the Virgin Islands, in the mid-1970s.

His suitcase loaded up with murder mysteries, Breit talked excitedly about the stories to his companions over dinner.

In Harry Kemelman's Rabbi Small series, the learned man used Talmudic reasoning to decode criminal motivation. Agatha Christie's Miss Marple sifted, ever observant, through small-town gossip.

But why, Breit lamented, were no economists represented in the genre?

"Bill is so creative," Elzinga recalled. "I said, 'You should create a character and do a mystery based on that idea.' He asked me if I would be willing to partner with him. Without much thought, based on the madness of the idea and affection for Bill, I said yes."

The team stayed on at the resort for an extra week, sketching out a plot based on characters they observed.

In "Murder at the Margin," a demanding hotel guest is done in. A former Supreme Court justice follows suit. Island police arrest the obvious suspects, but by applying his ever-ready economic principles, Spearman sniffs out the true killers.

The writers concocted a pseudonym by combining the names of two noted 19th century British economists, Alfred Marshall and William Stanley Jevons — just in case, Breit said, reviewers savaged their fiction.

First published by a small academic press in 1978, the Princeton University Press later reprinted the title.

"The Fatal Equilibrium," a tale of murder among Harvard's tenured professors, followed in 1985. A decade later "A Deadly Indifference" appeared.

The novels are used in beginning economics classes around the country and have been translated into several languages.

When not solving crimes, Spearman visits the legendary basement of Filene's department store to see what shoppers are doing with their consumer surplus. He muses upon the "interdependent utility function" he shares with his wife, a universally understood concept but, he concedes ruefully, less pop-song-friendly than love.

Actor and writer Ben Stein, host of the former Comedy Central quiz show and son of the late economist Herbert Stein, said in an e-mail that the novels are deftly crafted literature that professional crime writers would envy.

"But their insights and explanations about economics, and especially about economic teaching in the academy, are spectacular."