For all the horrifying variety of their specific crimes, most serial killers tend to have one thing in common: they operate near the margins of society.
And then there's Colonel Russell Williams.
"We're going to have to rewrite all of the books," said Elliott Leyton, author of the landmark study of serial killers Hunting Humans. "None of the serial killers I know of have been pilots for the Queen. None of them were photographed working with the prime minister or the minister of defence. None of them achieved the kind of high functioning position he did. He's a complete anomaly."
While most murders are committed by individuals facing chronic unemployment, with no education and a tendency toward drug and alcohol abuse, Dr. Leyton said serial killers are usually somewhat better off, coming from a working class or lower-middle class families.
But Col. Williams was not just scraping by, he was a senior ranking officer in the Armed Forces and was base commander of CFB Trenton at the time of his arrest.
"There's never been anything remotely resembling this," Dr. Leyton said. "The position he occupied in society is so central and so significant. He was on the margins of being a big shot and obviously knew how to carry off the whole charade."
It's not entirely unprecedented for serial killers to have jobs or be well regarded within their communities. Dr. Leyton points out that there have been a handful of murderous physicians, including Harold Shipman, who was convicted of 15 British murders in 2000 but is suspected of committing more than 200.
In the United States, Dennis Rader, known as the BTK strangler (so named in reference to his technique of "bind, torture, kill") was convicted in 2005 of killing 10 people in Kansas decades earlier. A married father of two, he worked for the City of Wichita and served on the council of his church for years before his arrest. He too had a fetish for women's underwear, often stealing them and wearing them himself, and served in the U.S Air Force for four years.
But Dr. Leyton said the small number of serial killers makes it impossible to draw any conclusion about their professional affiliations.
To understand what drove Col. Williams's actions or allowed him to rise to such a high rank in the military, he said more information is needed about his early life.
Most academic study of such criminals theorizes that people who go on to be serial killers are raised in homes with tremendous physical, sexual or verbal violence, where young people learn to anesthetize themselves against the feelings of others.
"They feel nothing for other people. Other people just become objects to relieve your long-suppressed rage and objects of your sexual fantasies," Dr. Leyton said.
Robert Pickton was raised in this kind of environment, he noted, before being convicted of murdering six Vancouver women.
Unfortunately, the opportunity to understand or question serial killers usually ends after they confess, he said, as Col. Williams did in his guilty plea on Monday.
"What we don't know is anything about him prior to the panty raids," Dr. Leyton said. "Until we learn something serious about him, all we know is that he's a bizarre anomaly."