Intro to Forensic Science and Bloodstain Pattern Analysis

Study Notes

Forensic science is the science of associating people, places, and things involved in criminal activities, assisting in investigating and adjudicating criminal and civil cases.
Forensic scientists have two major duties: performing scientific analysis of evidence and offering expert testimony in criminal and civil proceedings.
Educational requirements for forensic scientists have evolved from chemistry or biology majors without specific education in forensic sciences to undergraduate and graduate programs in forensic science.

Undergraduate programs in forensic science provide a strong foundation in chemical, mathematical, biological, and physical sciences, along with practical laboratory experience and coursework in law and criminal procedure.
Bachelor's degree programs include opportunities for hands-on training in forensic science laboratories.
Graduate programs, particularly at the master's level, have become more common, requiring a bachelor's degree in a science field and focusing on applying scientific principles to forensic work, along with coursework in law, criminal investigation, and criminal justice.

Bloodstain pattern analysis (BPA) is the analysis and interpretation of the dispersion, shape characteristics, volume, pattern, number, and relationship of bloodstains at a crime scene to reconstruct a process of events.

Passive bloodstains: clots, drops, flows, and pooling.
Transfer bloodstains: wipes, swipes, pattern transfers, and general contact bloodstains.
Projected or impact bloodstains: spatters, splashes, cast-off stains, and arterial spurts or gushes.
Wipe stain: created when an object moves through a pre-existing bloodstain.
Swipe stain: transfer of blood onto a target by a moving object that is itself bloodstained.
Spatter: a technical term describing stains resulting from blood hitting a target.
Forward spatter: blood droplets projected away from an item.
Back spatter: blood droplets being projected toward the item.
Cast-off stain: blood being flung or projected from a bloody object in motion or one that stops suddenly.
Arterial spurs/gushes: occur when an artery is breached while the heart is pumping; produces a zigzag, up-and-down pattern.
Voids: an indicator that some secondary object came between a blood spatter and the final target; leaves an outline or "shadow" on the final target.

The direction of a bloodstain can be determined to have originated at a point somewhere along that line.
Point-of-origin can be demonstrated by a convergence of lines (paths).
Presumptive serological tests can be employed to discover if the stain in question is truly blood.

Document the entire scene as discovered, including "establishing" photographs.
Photograph pattern transfers, pools, and other fragile patterns first.
Document patterns with "establishing" photographs that show the pattern's relationship to landmarks or other items of evidence.
Take macro and close-up photographs; include a scale in every photograph.
When reconstructing point-of-origin, document individual stains used in the reconstruction.

By finding the path for each bloodstain in a pattern, the analyst can interpret a point-of-origin.
The more paths that converge to this point, the more likely it is the actual point-of-origin.
The analyst must not be confused by multiple adjacent patterns, just because points converge doesn't mean that is the point-of-origin.
Stringing is a method of interpreting bloodstain patterns, using a string run from the presumptive source to the target, using push pins or masking tape to fasten the ends.