Introduction

In August of 2005 the author was contacted by an investigator with the State Attorney General's office in Denver regarding a three year old homicide case. The suspect(s) were believed to have painted over the bloodstained walls in the crime scene shortly after the murder. The author was asked to investigate the possibility of detecting blood under painted surfaces and recommend a method of searching for and detecting blood under these conditions. To assist with this experiment the investigator was able to search the crime scene residence and recover the original paint buckets utilized for the paint on the walls at the time of the homicide. The investigators went to a local paint store where a fresh gallon of similar paint and color formula was obtained.

A search of the forensic literature resulted in few references describing this type of research. Vandenberg and van Oorschot 1 reported on finding blood under paint using the Polilight™ PL500 at about 415nm. In their experiments it appears that blood was deposited directly on wood, plaster, brick, and metal and then painted over with various colors of light colored water based paint and white acrylic paint. Blood was visible under three coats of paint. From the photographs it appeared that the blood absorbed the ultraviolet light giving it a dark appearance. The authors also reported that blood could be detected under wallpaper using the Polilight™. The authors reported that a full DNA profile was obtained from blood samples under paint. Samples were subjected to Chelex™ DNA extraction and then amplified using Profiler Plus™. No attempt was made to scrape or separate the blood from the paint samples. Ray 2 also reported limited success in visualizing blood under painted surfaces 2. In her experiment the author placed both single blood drops and blood swipes on wood and then painted over the stains with up to three coats of a latex paint. An Omniprint™ 1000 and Polilight™ (150 watt model) were used to examine the stains under paint. Both units were set at 530nm. No statement was made regarding the type of filter used. The author reported that the bloodstains were “visible” to “barely visible” with the use of an alternate light source after two coats of paint were applied. The third coat of paint made the bloodstains either not visible or “questionable” in appearance with the light sources. None of the authors discussed methods for paint removal.

Experiment Design

A 4 ft. by 4 ft. section of half inch drywall was obtained for the experiment. No texture was applied to the wallboard. The wall was first painted with two coats of Glidden Speed-Wall interior PVA Primer #GL 1050-1200 white. The coats were allowed to completely dry at least 12 hours. After drying, two coats of Glidden Speed-Wall interior latex flat paint #GL 1251-0110 white paint were applied. All paint was applied using a clean paint pad. The wall was then allowed to dry overnight. Once dried, several different types of bloodstain patterns were produced on the wall (Figure 1). Bloodstain patterns included those not likely to be seen on vertical surfaces (such as blood dripping into blood). Blood droplets ranged in size from less than 1mm to over 12mm in diameter. The wall also contained partial bloody shoe impressions and vertical blood flow. Horse blood was used to create all bloodstains in the experiment. The blood was photographed and allowed to dry approximately 12 hours.

< read the complete article and view example photographs >

*Article submitted by the author