From investigating the shootings at Columbine High School to locating grave sites in the remote back country of the Rockies, Tom Adair has lived a life most crime authors only write about. While in law enforcement he was board certified as a senior crime scene analyst, was one of only 40 board-certified bloodstain pattern analysts and one of 80 board-certified footwear examiners worldwide. Over his 15 year career he has been interviewed by and consulted for television, text books, novels, magazines, and newspaper articles as well as documentaries on the Discovery Channel and National Geographic. He’s also the author of recent crime thrillers The Scent of Fear (2012) and Bloodlines (2013). He runs the BLOG forensics4fiction as a resource for authors to understand forensic science and law enforcement issues.
Bloodstain Pattern Analysis (BPA) is a critical component of Crime Scene Reconstruction (CSR). Many authors associate blood evidence with DNA but, DNA only answers the “who” question. The bloodstain patterns themselves may answer the “what”, “where”, “when”, and “how” questions. An analysis of bloodstains can reveal any number of issues such as the movements of bleeding subjects, sequencing of events, minimum number of bleeding subjects, minimum number of blows from a weapon, and much, much, more. It’s not uncommon for analysts to spend hours, even days, at a crime scene just examining the bloodstain patterns. I once spent nearly a week at the scene of a double homicide just documenting bloodstains! It can be very labor intensive but the work is rewarding if it clarifies critical questions.
One determination analysts may be tasked with is the determination of an “area of origin”. This is an approximate location in 3-dimensional space where a particular spatter pattern originated. This may be the relative position of a victim when they receive an injury that produces blood spatter on an adjacent surface like a wall. Determining this area of origin can shed light on a number of factors including the height of the event. You see, by measuring the shape and orientation of a blood drop we can determine the angle of impact (ex. traveling upward to the right at a 20 degree angle). When we compare the impact angles and directionality of several drops in a pattern we can back track the trajectories to a common convergence in space. This can provide critical information to investigators. For example, if the area is located a foot off the floor it’s proof that the victim was not standing or kneeling at the time the injury was inflicted.
But data on a page or spreadsheet doesn’t help others in understanding the nature of these convergences so analysts have developed ways to “demonstrate” this convergence visually. Modern techniques utilize computer programs and CAD programs to replicate these findings. The visuals can be helpful in court but they may come off as a bit “sterile” in my opinion. I’ve always preferred an older method called “stringing”. Essentially, after determining the angle of impact and directionality of the stain, the analyst attaches a colored “string” to the point of impact and runs it backwards to a termination point (like the floor). After attaching a number of these strings the area where all the strings cross can be photographed and used in other reconstruction events on scene. I should note that this process isn’t begun until all of the samples have been properly documented and collected. It is generally one of the last tasks done by the analyst.
The advantage to this technique is that the analyst can visualize this “event” in the real context of the crime scene and measure that event against other evidence found on scene. That process is more difficult on a computer screen back at the crime lab. Investigators can consider various scenarios and role play possible actions to create the blood patterns found in context of the actual crime scene. Now there are some limitations to this technique. It’s not useful for certain types of bloodstain events like passive staining, cast-off, or contact transfer stains. Also, blood droplets in flight eventually succumb to gravity and their flight path changes. Once that occurs back tracking that flight path becomes very difficult. Too many unknowns such as mass/velocity. Another “danger” is the possibility of some clumsy person damaging the strings during the process. What happens when a clumsy patrolman comes into the room and trips over your strings? Hours of work lost!
So if the injury occurs close (within a few feet) to the surface (wall, ceiling, furniture) then the technique can be very useful. The main thing to remember is that the results of such an exam are visually stunning and demonstrated in real space (the crime scene). The investigators can “see” the convergence from all angles and perspectives which is a wonderful tool in reconstruction. In the future we may see the ability for investigators to use holographic projections to simulate the findings thereby removing the possibility of inadvertently damaging the strings.
Here’s a blurb from Tom’s most recent release, Bloodlines:
CSI Sarah Richards is back in the heart pumping follow up to The Scent of Fear. Months after the assassination of Governor Hoines, a determined genealogist stumbles upon a conspiracy that threatens to expose a plot to reshape the nation by a rich and cunning family in Colorado. Now the Gerovit, an elite group of Russian assassins returns to destroy any evidence of the conspiracy. As Sarah’s mentor and his nephew Daniel crisscross the nation trying to unravel the genealogist’s coded journal, Sarah must discover how two double murders separated by a century are connected to the most powerful man in Colorado. But with enormous political forces, a team of killers, and her own department working against her, can Sarah unravel the clues before she becomes a part of history herself?
Some gals are musician groupies. Others are fascinated by all things Hollywood. For me, it’s forensics 🙂 Plotting that perfect crime? Wondering where TV gets it wrong? Fire away and Tom will try to answer your questions!