Vernon Geberth has a maxim for all young homicide detectives: “Do it right the first time. You won’t get a second chance.”

It’s a piece of wisdom the retired NYPD “murder cop” has imparted to some 70,000 investigators nationwide over his years in the business. Geberth himself got it right the first time, writing the textbook Practical Homicide Investigation in 1982, the first handbook to assist investigators in the practical aspects of solving violent killings in America.

More than three decades later, it's now commonly referred to as “the Bible of Homicide Investigation” – and he is still teaching detectives nationwide. In May, he published a fifth edition that’s essentially a whole new book, including advances in DNA and other technologies that were unthinkable 30 years ago.

“I’m at Mount Everest right now – I’ve reached the peak,” Geberth told Forensic Magazine in an exclusive interview this week. “It’s a culmination of many, many years.”

Read more: "Enter a New Era in Forensic Analysis"

The new edition of the book is a comprehensive study of murder, including Geberth’s collected wisdom of 46 years investigating the most horrific crimes imaginable. Packed with color illustrations of crime scenes, killers, and autopsies, it is a stark reminder of how frail life is, and the depravity that people are actually capable of.

Practical Homicide Investigation now runs more than 1,200 pages, and is updated to include the newest case histories, the latest developments in DNA testing, sex-related homicides, and even the intricacies of autoerotic asphyxiation, a growing phenomenon. The book has become like a “physicians’ desk reference” for homicide detectives.

But at its core is a principle of imposing order on the chaos, to clear crimes and serve justice. The text is written with a blunt honesty about how to handle the smell of decomposing bodies, to making death notifications to victims’ families, interrogating killers, and just about every other investigative responsibility.

Justice must prevail, Geberth concludes. A message that’s resonated with thousands of investigators across the country.

“He is an icon in homicide investigations,” said Anthony Ambrose, the chief of detectives for the Essex County Prosecutor’s Office in New Jersey.

From NYPD to the bookshelf

Geberth wrote the first edition of PHI in the early 1980s. He had read the criminology section of the library, and he saw that it had been decades since someone had written a practical guide to death investigation. Upon publication, his irate superiors asked who gave him the authority to write a book.

“ ‘First Amendment. Next question,’ ” Geberth recalls, laughing now. “They didn’t like that too much.”

He was punished with desk duty. But it was not for long – within a year, he was transferred back to investigating homicides in one of the most violent parts of NYC. He retired in 1990 as the commander of Bronx homicide, after overseeing 5,000 violent deaths.

But retirement was just the beginning. A second edition of PHI included information he wasn’t necessarily allowed to analyze while he was still within the NYPD.

Then came the O.J. Simpson trial. ​

Geberth became a “talking head” – an expert who would weigh in on the sensational trial for the TV show Inside Edition. Though approached by both sides in an expert capacity, he

 instead observed from the outside. The outcome of that criminal trial is still a sore point for Geberth.

Through his quarter-century of retirement, Geberth has added another 3,000 homicides to the total of deaths he’s investigated, and consulted on. But the ripple effect has magnified his influence, considering the tens of thousands of detectives he’s trained and assisted over the decades.

“I’ve probably solved more homicides in my second career than I ever did in my first,” Geberth said.

In the meantime, PHI kept growing with the complexity of modern detective work. The fourth edition, in 2006, was a complete overhaul, with the advent of DNA technology.

The fifth took more than three years to finish – partly because the nine years since the last one has brought a different world of criminal investigation. This time he’s employed experts to help write technical parts – like a microbiologist to explain the DNA specifics, and a forensic pathologist helped analyze modes of death from a medico-legal perspective, among other topics.

“A man’s got to know his limitations,” Geberth said.

‘We work for God’

Not many would agree with Geberth’s estimation of having self-limitations. Mark Czworniak, a recently-retired Chicago Police Department homicide detective, paid for his first seminar out of pocket in the 1990s, just after being promoted.

Czworniak became a disciple of Geberth’s – and even contributed a litany of crime-scene photos and a case history to the new edition of PHI.

“He’s always been the leader, as far as I know,” Czworniak told Forensic Magazine. “A lot of academics had published books on crime without having been an investigator. But Vernon had been there, and done that.”

But while he learned about processing crime scenes and interviewing suspects, Geberth’s philosophy is equally important. Homicide investigations in big cities like Chicago can be a discouraging enterprise, when witnesses won’t testify and convictions can be difficult. But Geberth’s guiding principle in PHI always kept things in perspective: “We work for God.”

The veteran detective was inspiring, the Chicago cop said.

“When I would go to Vernon’s seminars, I would always be re-validated in my work,” said Czworniak, himself now an instructor at the Chicago police academy.

A sixth edition isn’t on the horizon yet, Geberth said. But already he’s excited about some of the latest law enforcement innovations. He wishes he could have added DNA phenotyping – reconstructing faces just from genetic information – but it was too late for his deadline.

But PHI has taken on a life of its own, and it will grow as the profession grows, the veteran detective said.

“I don’t own the book,” Geberth said. “The book owns me.”