Intro to Forensic Science and Bloodstain Pattern Analysis

Forensic Science

• 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.

Educational Requirements

• 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

• 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.

Terminologies

• 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.

Point of Origin

• 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.

Documentation

• 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.

Point-of-Origin 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.