Cathie Louvet's chronicle


Folder n°1 : is the perfect crime possible?

With the ever-increasing progress of the scientific police, my friend Néville and I, in order not to be bored during the long winter evenings, decided to write a detective novel that directed The Crime Parfait. To carry out our project, we conducted our investigation.


Rule n°1: Prefer murder to murder: The proper thing of a perfect crime is never to get caught, it means leaving a number of indices and traces close to zero. Now, as Neville knows, when you commit a murder, that is to say without premeditation, the risks of leaving traces behind are legion: DNA, fingerprints, shoe marks, etc. Doug Lyle, an American expert in scientific investigation techniques that we consulted, who praises his services to writers of crime threats to help them design scenarios as close as possible to reality, said: "We forget crimes committed on a stroke of blood because a murder committed impulsively and thoughtlessly is necessarily sloppy !! " Okay, Doug, received message. So let's go for murder.


Rule n° 2 : The killer must be discreet: The killer must act alone. To have an accomplice is to multiply by two the risks of leaving traces, but it is also to be at the mercy of someone who can experience remorse and crack at any time, inexorably dragging you in its fall. Neville looked at me wrong. I know he thinks a woman is more fragile emotionally ... It does not matter, Neville, I let you determine the sex of our fictitious killer. "I remind you," continues Doug, impassively, "that the police investigation will not only scrutinize the gestures of the suspects after the crime, it will also look at everything they have done before." I imagine that the purchase of five liters of sulfuric acid or the sudden desire to pass the hunting license in order to buy a rifle may attract the curiosity of the investigators. Neville and I therefore agree: our perfect crime must be the work of a lonely assassin who will begin planning his plan a year before his execution!

Rule n ° 3: No staging in a foul: Do not try to make believe a natural death or a suicide; too complicated to stage and easy to detect. We who had imagined that our murderer would kill his victim with a stroke of candlestick and then to make him move down the staircase to make believe a fall! Doug explains: "This kind of make-up is impossible to carry out credibly, first of all, the wounds and the bumps of the corpse must correspond to the collapse supposed to have caused its death. quick." "Because, at the heart's stop, my little lady, the blood stops circulating and quickly escapes from the organs. He then leaves under the skin a characteristic mark, which the legists call "cadaveric lividity". This purplish mark is visible from the second hour after death, "I turn to my friend:" Did not you think of that, Neville? "" Of course that if, "replied the latter, vexed. depending on the area of ​​the body where the blood has been gravity deposited, investigators can determine the victim's position at the time of death. Thus, if the cadaveric lividity is on the left side of the body and the victim is found on the back, there is something suspicious! Also forget the false suicide with a pistol. During firing, residues of the explosive primer are thrown into a cloud on the person's hands, arms and clothing. If the "suicide" does not bear such traces, the police will quickly discover the pot with the roses.

Rule n° 4: Weapon or gun: Neville had a great idea for the weapon of the crime: an ice knife !! It melts from the crime accomplished so no footprints and well cut, it resists to the impact and easily crosses any piece of meat. "Well done, Neville, what a great idea," I said ironically. "It's nice, your ice knife, but you have to walk with a congel on your back. involves a physical confrontation with the victim, so risk of noise and splashing of blood everywhere. "Beurk !! ... To forget !!" A gun, then ?? Yes, on condition that the detonation is suppressed, knowing that a silencer can do nothing against the "bang" that the ball makes when it passes the sound barrier (340 m / s). Nowadays, most weapons have bullets at supersonic speed. So, what to do ?? The solution is to load the gun with ammunition containing less powder whose speed is lower than that of sound. But beware !! After his crime, our assassin must imperatively get rid of his weapon, as far as possible from the scene of the crime, which is not always easily realizable. In the sea, for example, or in the sewers. Because the link would soon be established between the bullet in the corpse and the pistol found in the suspect: indeed, the inside of the barrel of the weapon would betray it for sure! How are you going to tell me? As the weapon is used, small grains of sand, rust points, powder residues are encrusted inside the barrel. And the marks left by these impurities on the balls become more and more characteristic. This allows investigators to know whether the weapon discovered fired the bullet found at the scene of the crime or in a corpse.


Rule n°5: Do not sow your DNA. Unless we first cover the place of the murder of impermeable plastic from the floor to the ceiling (a solution that Neville and I consider practically unfeasible), Doug explained to us that it is more and more complicated not to leave traces on a stage of crime. "Until the early 2000s, we only worked on traces of so-called rich DNA," said Frédéric Dupuch, director of the National Institute of Forensic Science (INPS), that is to say samples such as blood, sperm, saliva that contain a lot of DNA. "But with increasingly sensitive reagents, modern techniques now allow DNA profiling from imperceptible drops of sweat on a clothing or some dead cells that have settled when rubbing the skin against a wall or furniture. Of course, our malefactor can always wear an integral suit and a hood, but he is not safe from a postilion or an eyelash that has fallen unfortunately. Of course, he can also choose to commit his crime in a public place (desert at the time of the crime) or his traces will be drowned among hundreds of other fingerprints, but he will have to find a pretext to attract his victim to this place desert. Neville has objected to me that this is not impracticable; he is right, but it complicates things. On the other hand, if he decides to operate with his victim, where the experts will have much more chance to trace his traces, it is better to make the body disappear.


Rule n° 6: Clean kill: Fingerprinting is a process that is a hundred years old, which does not mean that it has lost its effectiveness, quite the contrary! Thanks to the improvement of the quality of the chemical developer and the use of lasers, it is now possible to detect fingerprints on almost all surfaces: metal, plastic, glass, wood, cardboard, paper and even on the skin !! Soon, we will use "Roar particles": in the form of powders, these silica nanoparticles allow, according to their English designers, to detect chemical residues present on the fingers. It suffices to fix substances capable of attaching them to, for example, nicotine or cocaine, and then to recover the powder deposited on the impressions for analysis in a spectroscope (an apparatus capable of dispersing light reflected by a solid or a liquid, in order to identify the chemical elements that compose it. The investigators will thus be able to know if the person who left the fingerprints was a smoker or a drug addict, if he took medicines, etc. These particles would also be able to identify molecules secreted by the body and specific to each individual. This would determine the sex, age and ethnicity of the killer. Waouhhh, cried Neville. Scientists at the University of Leicester, England, have developed a technique that allows fingerprints to be recorded on the copper alloys that make up the bullet sleeves. Indeed, sweat can corrode some metals and literally engrave the fingerprints. Because even if the ball has been carefully cleaned, the corrosion remains ... and the imprints also inlaid !! So we thought with Neville that our killer should wear thick gloves to put the bullets in his gun; even if it is clear that this will complicate its manipulation ...


Rule n° 7: Make the body disappear: The most compromising index is obviously the body of the victim. As Neville said, no corpse, no evidence, so no murder !! "Certainly, but to make a body disappear is not so easy, dear Neville," I replied. In order to carry out our project, we therefore envisaged different solutions. The burn: the advantage is that fire destroys most DNA traces. But the disadvantage is that a human body, composed of about 70% water does not burn as easily as cigarette paper. According to the experts we consulted, for burning to be effective the body must burn at 800 degrees for at least two hours. And if gasoline is used, it must be known that it is an extremely volatile product, the vapors of which can ignite at the same time as the fuel and burn more or less seriously the person who sets the fire, which would compromise Rule No. 2. Dissolve it: acid is just as dangerous to handle as gasoline and less effective; in fact, our buddy Doug told us that a good week is necessary in order to completely dissolve a body in sulfuric acid or soda. Neville and I looked at each other, puzzled. We can not put this murderer to the risk ... Leave him at the bottom of a pond, grind it, cut it in pieces, bury it or have it devoured by pigs: whichever method is chosen, the murderer, who by principle always acts solo, will have to manage to transport the body to the appropriate place without being noticed and without involuntarily bringing a memory of his victim in the form of blood, saliva, hair, particles of earth, etc ...


Rule n° 8: No Perfect Crime Without Luck: Here is our final scenario: a solitary, methodical, organized killer, officially dressed in gloves, dressed in black clothes, armed with a pistol fitted with a silencer, in a public place leaving the corpse in place so as not to have to carry it in the trunk of his car, too compromising. Neville and I have realized that even a well-planned murder can not foresee everything: the splinter of the staircase ramp that cuts into its jacket; the passer-by who walks his dog; the car which passes near the wood in which it has attracted its victim; the footprints left by his shoes in a land rendered meuble by the rains of the last days ... In short, Néville and I concluded that to put together a perfect crime is very complicated. I think we will spend our evenings playing at the battle, it's less complex and less bloody ... though !!!

Cathie Louvet