Vidocq had many skills. He was excellent in concealing his appearance and identity, a good swordsman, an observant and perceptive person, a good forger, and knew how to keep his legend alive. But his biggest advantage was that he was a master criminal himself. He used all his skills while hunting other criminals.
Most of Vidocq’s cases involved catching petty criminals and political suspects. For this Vidocq trained his employees on using disguises and other undercover methods. Today such methods are common knowledge, but in the early 19th century, Vidocq was first to start the “French method of detective work” (An Introduction to Theory, Practice …).
Vidocq started the practice of plain cloths detectives when he was working in Sûreté. His reasoning was that people are more intimidated with uniforms and as a result not forthcoming. It is easy for plain cloths officers to merge in crowds without drawing attention to them.
Vidocq was once part of the criminal underworld, so he knew that everything in the criminal world was word-of-mouth and most criminals were known only by their aliases. To combat that Vidocq started the first criminal database. He started keeping files on each criminal by recording their alias, physical description, distinguishing marks, previous convictions, and modus operandi. Probably Vidocq was the first person to recognize that most criminals use the same techniques in most of their crimes.
Today every jury in every criminal trial wants forensic as shown on television crime shows. Forensic science is part of our common vernacular. Vidocq was the first person to invent a lot of these forensic methods.
At the scene of burglary, Vidocq found a footprint of the suspect in the garden. At that time, he had the suspect in his custody. He took the suspect’s boot and placed it on the footprint to match. This gave him the idea to have a cast made in plaster-of-Paris of the footprints or foot impressions.
Once while solving a murder, Vidocq had the suspect and the suspect’s pistol—a flintlock pistol. Vidocq took out the bullets from victim’s dead body. He placed them in the barrel of the flintlock pistol to conduct the first ballistics test.
As Vidocq was a master forger, once he forged papers to get this friend out of prison, he knew all the tricks of forgery. He funded chemists to develop indelible ink and unalterable bond paper. He held patents to both.
It is stated that he also developed the technique of handwriting analysis. But apart from one online article, I have not found any other evidence of that claim.
Until now, I didn’t realize the popularity of Eugène François Vidocq in present times. I learned about The Vidocq Society. In 1990 three people, a former FBI agent, an advertising photographer and a commercial diver, and a criminal psychologist formed a think-tank for unsolved murders. They call themselves Vidocqians and they follow the principles of detecting invented by Vidocq.