CAUGHT ON (VERY FAST) CAMERA
From striking hammers to speeding bullets, incredibly high speed digital photography and video is capturing visual proof of how, why, when and where blood can spatter.
One-millionth of a second. That’s how fast Dr Michael Taylor has been working – taking digital photographs to capture the actual formation of bloodstain patterns. When it comes to digital video, the camera’s been rolling at up to 20,000 frames a second, 800 times faster than your home handi-cam.
“There are a whole bunch of variables that influence how blood spatters. Understanding of the dynamics is critical to the sound interpretation of bloodstain patterns. High-speed photography allows scientists to acutally see what actually happens. Around the world, very little has been documented about the dynamics of blood transfer. “We’re producing information that can be used in court. It’s the science that underpins the evidence that is presented.”
Dr Taylor, collaborated with a team at the Minnesota Bureau of Criminal Apprehension (BCA), the state forensic laboratory, helping to produce a series of high-speed video sequences that are now available to the international forensic science community, via the internet. In New Zealand the research has also involved collaboration with the Universities of Canterbury and Otago.
Video sequences included a falling drop of blood; a hammer striking a pool of blood; a finger being wiped through blood; ‘expirated’ blood spray being breathed out by someone with a head injury; and a bullet passing through a bloody sponge to replicate ‘backspatter’. Some of these sequences have since been used to aid courtroom understanding in the 2009 retrial of record producer and songwriter Phil Spector, convicted of second-degree murder.
Blood backspatter
The scientists are trying to understand more about blood backspatter, occurring when someone is shot. It is well known that blood projects back towards the person holding the gun, so if they are standing close by, this can lead to incriminating evidence. The Minnesota research revealed a previously unknown phenomenon: the distribution of backspatter is influenced by gases from the gun barrel.
Shadowgraphy
‘Shadowgraphy’ is essentially the same process as forming a hand shadow using a bright light. Shadowgraphy allows fleeting air density changes and movements that influence backspatter to be caught on camera.
The images show that gases have a huge effect on backspatter. The gases travel a few microseconds behind the bullet. They have a dramatic interaction with the airborne blood droplets. Most droplets are effectively swept forward instead of back.
Any bloodstain pattern produced by backspatter from a gunshot wound could well be influenced. Dr Taylor says that in criminal trials, great care should be taken in attaching significance to the absence of backspatter on an accused person or a firearm. This could simply be the result of the sweeping effect of air currents.”
Unravelling the mechanism of wounding
The mechanism of wounding is now coming under the spotlight. (Literally so - high speed camera work requires extremely bright lighting.) The path of a bullet passing into the brain opens up a temporary cavity, which then shrinks, and is replaced microseconds later by a permanent cavity – all influencing spatter.
“How and when does this happen? When we unravel the mechanism, we’ll be in a better position to say when to expect blood spatter, and when not,” Dr Taylor said.
This imaging work is still in the early stages. It involves intricate model making, with polyurethane resin skulls, foam rubber flesh and gelatine brains. There’s a lot of work, and much validation, yet to be completed but the prospects for courtroom forensic knowledge are exciting. “Using models to understand the dynamics of wounding is never going to be perfect. But it will be a lot better than what the courts have now – which is limited.”
Model making is also helping build greater understanding of stains from expirated blood. Again, this can prove crucial in a criminal case, as a bloodstain can be very similar to that from an initial wounding event. Determining guilt or innocence can depend on being able to distinguish the difference.
