Correction: A previous version of this article included an outdated description of Apsche’s employment. The article described him as an employee of the Ross Center for Anxiety and Related Disorders in Northwest Washington, but Apsche left the center in early October and is no longer affiliated with it. This version has been updated.

Jack Apsche is one of the few people in history happy to have crossed paths with a serial killer.

That was Gary Heidnik, who tortured six women and killed two, and was one of the inspirations for the Buffalo Bill character in “The Silence of the Lambs.” Heidnik, who was arrested in 1987, was considered inscrutable even by sociopathic standards. More than 150 mental health workers in 22 hospitals interviewed him during his life. But perhaps the individual Heidnik most revealed himself to was Apsche.

The interactions of the two men are a bizarre and intriguing tale of depravity and redemption, resulting in the creation of an experimental psychological technique that Apsche now touts as a treatment for others whose lives have spun out of control.

Now 65, Apsche worked at the Ross Center for Anxiety and Related Disorders on Wisconsin Avenue in Friendship Heights until early October, a specialist in treating troubled, often violent young men. He commuted from Shepherdstown, W.Va., where he lives with his daughter, wife and seven dogs. Apsche has a gruff demeanor nurtured by years of drug use, violent outbursts and 20 months of service in the Vietnam War. Though now an esteemed psychologist, when he was hired as a researcher for Heidnik’s defense, Apsche, who had just received his PhD in counseling psychology, says he was addicted to sex, suffering from nightly combat flashbacks and battling a cocaine addiction.

These days, Apsche looks back on the case as a lifeline. “Gary Heidnik and September 1987 was an absolute turning point for me,” Apsche writes in a book he recently completed and is hoping to publish about his relationship with Heidnik. Immersing himself in the proceedings gave Apsche a sense of purpose and spurred him toward self-reflection. “By looking into my own scared and desperate experience, I could better understand what was driving Heidnik’s obsessions and sexual violence,” Apsche writes.

A meeting that resonated

Perhaps it was Apsche’s own coarseness that appealed to Heidnik. The first time they met, in a small room at Holmesburg prison in Philadelphia, Apsche remembers being annoyed by Heidnik’s evasions.

“Listen, when I was in Vietnam, I killed more people than the Manson family, so let’s cut the s---,” Apsche says he told the murderer.

Perhaps their similarities resonated. Both were poor husbands and fathers, Apsche now recalls, prone to grandiose thinking and depressed, disturbed, violent individuals who engaged in obsessive sexual behavior.

Whatever the reasons, over the next three years, while on death row, Heidnik exchanged 26 letters with Apsche. The more than 150 handwritten pages of letters provide harrowing insights into the mind of one of the most perverse killers in U.S. history. Among Heidnik’s writings are drawings of the torture chambers he dug under his house, as well as descriptions of his crimes. They are now the basis for Apsche’s book, tentatively titled “Greetings From the Crypt” — an opening line in one of the condemned man’s letters.

The letters changed Apsche’s life. He quit cocaine, booze and womanizing, got remarried and regained custody of his daughter. He is now the pioneer of a psychotherapeutic approach known as mode deactivation therapy, a technique for treating angry, sexually disturbed patients. There is no doubt, Apsche says in a series of interviews, that the MDT approach depends, to some extent, on the understanding of human nature he gained through interacting with Heidnik.

‘The consummate expert’

Apsche encountered Heidnik shortly after completing his doctorate in counseling psychology at Temple University in Philadelphia, the city where Heidnik committed his crimes. In September 1987, Heidnik’s attorney hired him as a researcher on the case. (Apsche was friends with the lawyer’s cousin, “and they saw that I was smart,” he says.) He spent three months poring over two boxes filled with Heidnik’s arrest records and psychiatric reports in an attempt to ascertain the killer’s mental state.

Apsche was convinced that he could understand Heidnik as nobody else. “To make up for my lack of experience, I determined that I would become the consummate expert on Gary M. Heidnik and serial murderers,” he writes in his book. “I dedicated myself to learning and knowing more about the subject than anyone else in the world. And I did.” Thousands of experts across the globe study sociopathic killers, of course, and it says something about Apsche that he rates himself the best.

Heidnik’s attorney claimed insanity, and Apsche testified to that effect for a day and a half. “I was originally only hired as a researcher, but because I knew more about Heidnik than anyone else, I was asked to testify,” he says with characteristic bravado. But Heidnik’s intelligence and articulateness, combined with the premeditated nature of his crimes, convinced the jury of his competence, and he was sentenced to death. Apsche, who maintains that Heidnik was, indeed, mentally ill — says jurors rarely accept the insanity defense for people such as Heidnik because they are “so seemingly adept at finding victims and concealing their grisly crimes, and so skilled and diabolical in their detailed planning and deception, that ordinary people cannot believe the killer was not clearly in control of his actions.”

After the trial, the young psychologist proposed writing a book on the killer, and Heidnik agreed to cooperate. The men had a “unique trust,” says Apsche, who admits he empathized with the killer, whom he viewed as beset by powerful internal demons. They met five or six times in prison, for two-hour sessions, and traded the letters. Ranging from one to 28 pages, the condemned man’s letters are penned in blue ink on yellow legal-size paper. Their tone oscillates between hostility and friendliness, and they are filled with spelling mistakes, grammatical errors and smiley faces.

Read cumulatively, Heidnik’s letters — self-absorbed and wholly lacking in empathy — illustrate how the mind of a tormenter works. He repeatedly and passionately denies being a serial killer. “Those two deaths were purely accidental,” he says. “There was no willful intent or premeditation on my part to kill anyone.” He says more than once that if he wanted to kill the women, he would have used a different method. In Heidnik’s mind, the fact that he kept his victims locked in a cell, tortured and starving for months, was simply incidental to their deaths. The single most disturbing letter contains a hand drawing of Heidnik’s dungeon. “From purely the technical aspect neither death seems possible,” he writes.

After three years, the letters stopped. Apsche thinks it was because he was homing in on “what was really going on” with Heidnik. “I was asking him questions nobody else was,” Apsche says, “and could relate to him in ways others couldn’t, forcing him to confront what he was and what he’d done.”

Eight years later, in July 1999, Heidnik was executed at a state prison in Rockview, Pa. After consuming two cups of black coffee and two slices of cheese pizza, he was put to death by lethal injection.

As Gary Heidnik’s life was ending, Jack Apsche’s was beginning.

Belief in redemption

Apsche says that working with Heidnik helped him understand troubled psyches. “I realized that most people are redeemable,” he says. “Heidnik was on the end of the spectrum as far as evil goes, and most people, even ones that seem like a lost cause to most others, can be redeemed.” Apsche was motivated to work with kids, haunted by them. He saw similarities in the acutely troubled young men he worked with and those with whom he had served in Vietnam, people who had committed and been exposed to unimaginable violence.

Apsche now works with aggressive, inner-city 14- to 18-year-olds. “If a kid is tough, you can’t out-bully him,” Apsche says. “This boot-camp bulls--- you see on TV only makes them more aggressive.” Most of the kids aren’t sociopathic, despite their appearances, he says. There are kids so far gone they can’t be helped, he admits. But most can advance. One youth Aspche counseled, who physically assaulted staff members at a mental health institution, was reacting to his own fears, Apsche theorized. His parents had subjected him to unimaginable abuse. After receiving MDT counseling — which combines behavioral science with concepts of acceptance and mindfulness, derived from Eastern and Western meditative practices — the boy changed, Apsche says, eventually enlisting in the Marines.

A series of 20 studies, conducted mostly by Apsche and published in the peer-reviewed International Journal of Behavorial Consultation and Therapy, or JBCT, showed MDT to be effective in treating both young sexual offenders and violent ones. After two years of treatment, fewer than 10 percent committed offenses again. Only severely depressed youngsters proved immune to MDT’s benefits, Apsche says.

It’s effective “because it combines a number of approaches,” says Scott Zeiter, the former chief executive of North Spring Behavioral Health Care in Leesburg. “Here you have all these kids that society struggles with — and with Jack they’re doing mindfulness techniques in the corner.” The kids get a sense that Apsche is authentic, says Zeiter, who hired Apsche several years ago to work at the facility.

MDT has yet to become well-known enough to elicit significant critical appraisal. Says Stephen Hayes, a psychologist at the University of Nevada: “The first book [on MDT] just appeared, and that is usually when the critics start showing up.” One recent review in a behavioral-therapy journal holds that problems such as small sample sizes and lack of random subjects in existing MDT studies must be considered, even as the article finds that the effectiveness of the approach is “overwhelming.”

“Thousands of new psychological approaches” crop up all the time, “but only a handful are effective” says Joseph D. Cautilli, editor of JBCT. Cautilli carried out an independent evaluation of MDT and said he found it to be one of those rare treatments.

Final business

In 2010, Apsche turned to his long-unfinished business — writing the Heidnik book. “It was the last part of moving on,” he says now.

Twenty-five years after the Heidnik case, Apsche has built himself a successful life. Gone are the drunken, cocaine-fueled nights that saw him in bed with strippers until sunrise.

“For better or worse, Heidnik was my dark companion on the journey to health,” Apsche writes. Heidnik destroyed many lives. But, in his years on death row, he inadvertently saved Jack Apsche’s.