On April 30th, Dave Exline, Senior V.P. and Cara Plese, M.S., Scientist I at Gateway Analytical hosted a webinar designed for police and attorneys involved in cases with physical evidence. During this webinar, our presenters discussed the advantages of microscopic and presumptive screenings of physical evidence, especially suspected bodily fluid stains and hair prior to advancing to more expensive DNA analysis. They also provide examples of such screenings and discussed how these screening methods can save valuable time, money and resources by eliminating samples from being forwarded onto unnecessary further analysis.
For more details on the webinar, you can use the links below.
We received a number of questions from attendees during the Q&A segment, and you can find those questions and answers below. If you have any questions about this or any other topic, please contact us.
- How long does it typically take to screen evidence such as hairs and fibers?
The initial screening to determine if a hair is a human hair, or to determine if a root suitable for nuclear DNA is present takes only a few minutes. A more in depth analysis to determine the species of an animal hair, or to compare questioned to known hairs will take longer.
- If optical analysis is a screening tool for condom lubricants, what is the confirmatory test?
The condom lubricant test is a two part examination. The screening for starch is performed along with FTIR analysis to detect the presence of polydimethylsiloxane (PDMS), which is a commonly used dry lubricant. Both starch particles and PDMS must be present for the result to be considered positive.
- Are there other types of presumptive biological tests that you did not cover? Is there a good reference for those tests?
Yes, there are several color tests that use reagents such as Amido Black and Leuco-Crystal Violet which turn a specific color when they interact with blood. These particular reagents are commonly used at crime scenes to enhance blood patterns such as fingerprints or footprints left in blood. Resource Link
- How long does it take to do a test for blood using the ABA Card?
The ABA card tests for both blood and seminal fluid take 10 minutes, at most. Once the sample has soaked in the buffer (5-30 minutes depending on the age of the stain) a portion of the buffer is transferred to the test card. If a positive result is not present by ten minutes, the test is considered to be negative.
- Why do optical screening on human hair if everything can just be identified with DNA?
Optical screening of hair can be very valuable when determining which samples to forward on for DNA testing. The optical examination can determine which hairs would be the best candidates for nuclear DNA testing based on the root phase, and can also weed out hairs that are not human in origin.
- What, if any, qualifiers do you give when dealing with racial and body area origin?
The majority of hairs exhibit characteristics that can be classified into racial and body origin, however, there may be an overlapping of characteristics that don’t allow for this and must be qualified.
- What type of microscope do you use to analyse hair samples to separate it from animal hair?
A compound microscope is used for most hair analysis. A comparison microscope is used when comparing questioned to known hairs.
- What is the rule in regards to presumptive screening with gunshot residue? Does collecting a presumptive sample affect your SEM analysis?
The general rule for using ICP or other presumptive testing methods is to collect a sample for presumptive testing at the same time but independent of the sample being analyzed with SEM/EDS.
- Do some types of hairs have overlapping characteristics such as pubic hairs vs underarm hairs and chest hairs?
Yes. Especially is transitional regions, there will be overlapping characteristics in different types of body hairs. Specifically with underarm hairs, you may see bleaching due to deodorants which you typically wouldn’t see in hairs from other areas on the body.
- How long is training program to teach someone to screen hairs?
A scientist can be trained in a couple days to conduct presumptive testing of hairs. In order to conduct full hair comparisons, the training can be several months to a year.