Reliability of blood spatter analyses questioned

Come across a grisly bloodstained crime scene or a ghastly accident and who do you turn to? You get in touch with a team of highly qualified specialists in Christchurch who have mastered the arcane discipline of reading bloodstains or, as they call it, Blood Pattern Analysis.

Show them a bloody scene and they will note the victim’s position and location; record the size, shape, position, distribution, age, spatter and transfer of the stains; calculate the angle and force at which victim was hit and deduce the weapon used. Their observations and measurements help the police to reconstruct events leading to the bloodshed, and to find the cause of death or injury.

The first person to scientifically analyse bloodstains was the Pole Eduard Piotrowski, who in the 1800s covered the walls of a room with white paper, then beat rabbits to death to see how the blood splattered. He found that blood rarely appears until the second blow.

Analysts followed in each other’s footsteps for nearly two centuries. Despite progress over recent years, analysis relied heavily on the experience of forensic investigators rather than a clear understanding of underlying scientific facts. Mistakes are sometimes made, resulting in serious miscarriages of justice.

‘‘Until the recent past’’, says Dr Michael Taylor, who leads a team of investigators at the Environmental Scientific Research Institute in central Christchurch, ‘‘there was very little scientific research happening because most people in the discipline were up to their eyeballs in casework’’.

As so little research was being done, Taylor and his team recently set about testing the competence of 27 well-established practising professional analysts from Europe, America, Australia and New Zealand.

He invited them to pass judgment on photos of 13 different blood-stained scenes – some caused by blood flying off different weapons such as a knives, or a cloth-covered spanner. The specialists got 87 per cent of the scenes correct but 13 per cent wrong.

It got worse when analysts were given additional information about the crime scene. They got 20 per cent wrong. When Taylor extended reliability judgments to bloodstained fabrics, the error rate jumped to 23 per cent. These revelations were a massive wakeup call in the world of Blood Pattern Analysis.

One of the Christchurch team is Dr Nikola Osborne, who is particularly interested in how contextual information about a crime scene can influence forensic decision-making. She says analysts rarely go into a crime scene blind.

‘‘You can’t ignore the body on the floor, the mess in the house. You can’t operate in a vacuum,’’ she told the journal The extra information often overrides the bloodstain evidence.

Osborne also finds that two investigators are more likely to say that two fingerprints match when they view highly emotional crime scene photographs immediately beforehand.

The same influences probably affect all forensic disciplines – handwriting analysis, forensic anthropology, shoe print and bullet comparisons, and DNA interpretations. Says Osborne: ‘‘Nobody gets bored when I tell them my work stories’’.

Collectively Taylor’s team aims to root subjective practices out of Blood Pattern Analyses.

For it to work effectively, ‘‘its lexicon will need to be evaluated,’’ says Taylor.

"You can't ignore the body on the floor, the mess in the house. You can't operate in a vacuum."

Dr Nikola Osborne