Chemical Enhancement Techniques of Bloodstain Patterns and DNA Recovery After Fire Exposure*

Abstract

It is common in forensic casework to encounter situations where the suspect has set a fire to cover up or destroy possible evidence. While bloodstain pattern interpretation, chemical enhancement of blood, and recovery of deoxyribonucleic acid (DNA) from bloodstains is well documented in the literature, very little information is known about the effects of heat or fire on these types of examinations. In this study, a variety of known types of bloodstain patterns were created in a four-room structure containing typical household objects and furnishings. The structure was allowed to burn to flashover and then it was extinguished by firefighters using water. Once the structure cooled over night, the interior was examined using a bright light. The bloodstains were evaluated to see if the heat or fire had caused any changes to the patterns that would inhibit interpretation. Bloodstain patterns remained visible and intact inside the structure and on furnishings unless the surface that held the blood was totally burned away. Additionally, a variety of chemical techniques were utilized to better visualize the patterns and determine the possible presence of blood after the fire. The soot from the fire formed a physical barrier that initially interfered with chemical enhancement of blood. However, when the soot was removed using water or alcohol, the chemicals used, fluorescein, luminol, Bluestar, and Hemastix, performed adequately in most of the tests. Prior to DNA testing, the combined phenolphthalein/tetramethyl benzidine presumptive test for the presence of blood was conducted in the laboratory on samples recovered from the structure in an effort to assess the effectiveness of using this type of testing as a screening tool. Test results demonstrated that reliance on obtaining a positive presumptive result for blood before proceeding with DNA testing could result in the failure to obtain useful typing results. Finally, two DNA recovery methods (swabbing the stain plus cutting or scraping the stain) were attempted to evaluate their performance in recovering samples in an arson investigation. Recovery of DNA was more successful in some instances with the swabbing method, and in other instances with the cutting/scraping method. Therefore, it is recommended that both methods be used. For the most part, the recovered DNA seemed to be unaffected by the heat, until the temperature was 800 degrees C or greater. At this temperature, no DNA profiles were obtained.

Evaluation of Bluestar® Forensic Magnum and Other Traditional Blood Detection Methods on Bloodstained Wood Subjected to a Variety of Burn Conditions,

“…This is problematic as many laboratories require a positive presumptive blood test on a suspected blood sample prior to DNA testing. Some laboratories take this a step further and require a positive microchemical/hemochromogen presumptive test (e.g., phenolphthalein and TMB) regardless of if a positive result was obtained from a blood enhancement test (e.g., luminol and fluorescein) —likely because the latter are more subject to false positives. If this policy is strictly adhered to, many samples with potentially informative DNA profiles will go untested.…”

“…It has also been noted that Bluestar ® Forensic Latent Bloodstain Reagent (abbreviated as “Bluestar”; Bluestar ® , Monte‐Carlo, Monaco) and luminol can interfere with subsequent phenolphthalein or tetramethylbenzidine (TMB) testing for blood samples more dilute than 1:100 . A combined phenolphthalein tetramethylbenzidine (PTMB) has also been adopted by a small percentage of forensic laboratories and/or cited in the literature . This combined test is advantageous because it provides both basic (with phenolphthalein) and acidic (with TMB) testing environments, which eliminates false positives that may occur in either condition.…”

“…Studies involving the effects of fire on biological evidence have demonstrated that extreme heat, close proximity to fire, and presence of soot negatively impact the sensitivity of presumptive blood tests and/or to obtain full DNA profiles, especially from combustible substrates . Researchers have attempted to combat soot from interfering with presumptive blood tests by wiping it away , but this does not seem to be an effective approach for combustible substrates such as wood. Interestingly, full DNA profiles have been obtained from samples failing to yield a positive presumptive blood test , extinguished via water by firefighters , and even from noncombustible and nonabsorbent samples exposed to temperatures of 1000°C .…”

Developments in the chemistry and applications of phthalein dyes. Part 2: biological applications

“…Furthermore, fires have been used by perpetrators to cover up homicides and other violent crimes. Bloodstain pattern interpretation and recovery of DNA from bloodstains were carried out using phenolphthalein‐based chemical techniques . The combined phenolphthalein/tetramethylbenzidine (TMB) presumptive test for blood was conducted prior to DNA testing, and 55% of a full DNA profile was obtained.…”

Preliminary Study on the Effect of Heated Surfaces Upon Bloodstain Pattern Analysis

“…Further investigation into this reduction was carried out by centrifuging the blood separating it into TABLE 1--Release heights of blood drops calculated from the tip of the pipette to the impacting surface and transfigured into impact velocity with the use of Eq. (7).…”