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Scientists discover why murderers sometimes don’t get covered in blood

Scientists have discovered that blood from gunshot wounds does not always land on the killer - Monty Rakusen/Digital Vision
Scientists have discovered that blood from gunshot wounds does not always land on the killer - Monty Rakusen/Digital Vision

Getting away with murder just became harder after scientists discovered that blood from gunshot wounds does not always land on the killer.

Experts found that when bullets are fired they create a spinning column of air and propellant gases between the victim and shooter, which can pull blood splatter backwards towards the target.

It means that a killer standing near a victim may barely get splashed with blood at all, as the initial impact forces the spatter out in a cone-shaped mist - either side of the shooter - while the vortex effect sucks any central particles back the way they came.

The team of US researchers said it could explain how Phil Spector, the American music producer, managed to stay relatively clean of blood stains after murdering Lana Clarkson by firing a revolver in her mouth in 2003.

Spector had just 18 tiny drops of blood on his jacket, and his defence team claimed there should have been more if he had been in close proximity to the actress when she died.

Although ultimately convicted of the killing, the first trial ended with a hung jury in part because forensic experts could not agree how to interpret the blood spatter evidence.

But the new research shows how blood can miss the shooter and even end up behind the victim.

“Muzzle gases form a turbulent vortex ring which moves toward a victim from a shooter and pushes the blood droplets from the shooter back to the victim,” said author Alexander Yarin, a specialist in fluid dynamics, who hopes the findings could produce a computer analysis tool for use in crime scenes.

“Droplets are also deflected aside, and our predictions showed that some can even land behind the victim, even though initially they were moving from the victim toward the shooter.

“Hopefully, code based on the present results would be used in future crime scene investigations.”

The team made the discoveries by shooting bullets through sponges soaked in pigs blood, filming the spatter with high-speed cameras and capturing the spray on white paper.

Blood can be tricky to interpret because it has far more complex properties than other fluids, such as water, and can flow, drip, spray, spurt, gush or ooze from the body depending on the wound.

It is also non-Newtonian fluid, becoming less viscous when more force is applied, which helps blood flow quickly into veins when exercising, but can make its behaviour difficult to predict as it leaves the body at speed.

It also coagulates quickly and has elastic properties, allowing it to deform then return to its original position, all of which are affected by the surface on which it lands.

In a gunshot wound, the blood initially sprays out in a process called “primary atmonsition” which results in multiple drops flying through the air.

Larger drops are distorted by air and drag forces creating secondary smaller droplets, in what is known as “secondary atomisation”.

It is that secondary phase that is disturbed by the turbulent vortex rings produced from the end of a gun after it fires.

The swirling gas can either propel the blood droplets further from the target than expected, or turn them backwards towards the victim, with many landing on the floor between the shooter and the target, video footage showed.

In Spector’s case, it meant the droplets could have passed by him or even turned backwards towards Miss Clarkson.

The effect is driven by a phenomenon known as the Rayleigh-Taylor instability which occurs when a denser fluid accelerates towards a lighter fluid or gas.

The team is now planning to study whether the spatter of brain tissue may also follow similar patterns, which could help determine whether a person killed themselves, or had been murdered.

The new research was published in the journal Physics of Fluids.