jimtrue.com : school : CJT2260 : 2003-08-28: Intro to Biological Evidence
Posted by Jim True on August 28, 2003 4:16 AM. Last Updated October 22, 2006 9:23 PM
Disclaimer for all material noted here is at the bottom of this web page.
*Biological Evidence* -- First class meeting.
Tracy Messina, 3rd year teaching at Allstate Center in classroom and online.
Biological Evidence Examples
Saliva -- chewing gum, beverage containers, straws, stamps, envelopes; DNa comes from the cells in the mouth that has sloughed off, not from the fluid itself.
Plants -- plant material lodged in clothing, trucks, tires, etc.
Fingernails -- scrapings after a rape.
Seminal Fluid -- DNA in Spermatazoa; Secretors will be provide ABO typing; can also find shed skin cells from urethra, etc.
Primarily dealing with the *Identification and Individualization of human tissues*.
Identification -- Serology, serological groupings (Class characteristics); Identification of *tissues*, not identification of the person. Class can only be used to Exonerate or Exclude individuals; not as discriminating to individualize.
Individualization -- DNA. Can usually take a very small sample of DNA (about the size of a pinhead) and match it to a specific person. Can be used to Convict, Exonerate or Exclude.
Probitive value of evidence; The Lab must provide statistical data, explaining importance of the probative value of the evidence. Lab person will provide information to Judge and Jury.
*Blood Types:*
0 -- 45%
A -- 40%
B -- 10%
AB -- 5%
ie: piece of gum goes through serological testing, person who chewed the gum had type B blood, 10%. RH factor (positive is 85%, negative is 15%)
10% x 15%. Further narrowing by saying which percentage of the population had access to the crime scene.
If good tests are run, once evidence has been collected and documented correctly, we can run statistical data and increase the probative value of our evidence based on this data. Probative Value is the ability to PROVE that a crime did or did not occur.
Discriminatory power of our tests, or how well the tests can individualize evidence to a particular person. This will depend on types of tests that are run against the evidence. Quantity and Quality of your evidence.
In the mid-80's, RFLP was developed by Alec Jeoffries, referred to as DNA fingerprinting. This particular type of test required a rather large sample of biological material. High Molecular Weight (HMW) DNA; biological materials begin to degrade and breakdown after leaving the body. Some factors will accelerate this decomposition: heat and humidity. Also time will factor into this degradation.
HMW Quality is a very long, nice strand of DNA. Over time it will start to fragment.
If you don't want your DNA to degrade into little tiny pieces, you will want to concentrate on *Preservation* of your evidence. It will need to last until it gets to the lab and until it can be tested.
In order to preserve evidence, you will first need to:
Recognition, that you actually have evidence.
Documentation will have to be performed, video, photography, sketches
Collection & Preservation (most critical to trace evidence) Easier to see trace evidence with white light at an oblique angle (hairs & fibers), or a UV ALS.
After Evidence has been collected, evidence will be *tested*.
After Testing, *Interpretation* stage begins. Responsibility of the Lab and the Criminalists will preserve and make proper interpretation of evidence.
To be properly interpreted, it must be objective; those findings must be explainable to a judge and jury.
*Finding Evidence*
Particularly with trace evidence, salivary or seminal stains, you just have to know where to look. You won't be able to see it, but you'll have a pretty good idea that it's there.
Also have to know HOW to look. Sequential processing. Doing the least damaging tests first; don't want your first test to be your last test.
"Visual" Exam. Oblique lighting, ALS. You aren't harming the evidence this way.
Presumptive Testing
Indirect tests will be the least damaging. You will be transferring biological material away from it's source location onto another surface and not destroying the entire sample, ie KM, or Kastle-Meyer. Phenolphthalein.
Direct Tests, just the opposite will be applying the reagents DIRECTLY onto the area where you believe there is evidence. Luminol is an example.
Next class period will be working with KM.
Interpretations with these presumptive tests will go one of three ways: Positive Indication, Negative Indication or Inconclusive (No conclusion).
False Positive and False Negatives. Reaction on the swab that will indicate blood is present, but it isn't there. Negative would be a reaction that blood is not present, but it IS present. False negatives will sometimes happen if the sample is too dilute or degraded.
Documentation - if you are going to photo or video something, you don't want to make it appear that the scene has been tampered with. First photograph must be without a scale, and second without a scale of reference.
Class will be about the types of tests the labs are doing; what evidence to collect first and preserve, and how to avoid damaging that evidence. Strengths & limitations of presumptive tests.
Collection of Evidence
Nature,
Location,
Fragility, biological evidence is the most fragile evidence there is, with the exception of hair, DNA from the root fragment or follicular tag.
Examples, called out to a scene, out by a road-side ditch, looking for a gun thrown out into the water. gun has been there a number of days. Remove it from where it's sitting and put it in a container of the same material, otherwise the gun will rust and oxidize. Must keep the gun wet until it's analyzed.
Blood/Biological fluids, have to dry them up before sending them off to the lab because the dried sample will be more stable. Must be in a porous container; if they are in an airtight container, moisture will form which will decompose the material. No airtight packaging.
Exception: Blood mixed with soil -- bacteria, molds, etc., will be in the soil. Put this in a glass test tube and freeze it. Retard the decomposition.
Jeans or clothing soaked with blood, the clothing will soak through a porous container and might contaminate the scene. Take a plastic bag and put the clothing in a plastic bag to prevent it from running everywhere. Plastic is 'temporary' until the evidence can be properly dried. Then can be packaged in paper in it's primary container, within it's secondary container. Cannot be STORED in plastic, but can temporarily transport in plastic to prevent contamination.
Example, baseball bat murder. Gun has blood and hairs. Leave the evidence intact, take the baseball bat and allow it dry. Don't pick hair or evidence off the weapon.
Confirmatory Tests -- Lab will perform these. Blood. KM is a pretty reliable presumptive test for blood. Microcrystalline tests, Hemoglobin to react with a series of reagents. Takeyama test. Reddish rhomboid crystals. Seeing those crystals are Confirmatory for blood.
Semen - Acid Phosphatase is presumptive; confirmatory for semen is physical inspection looking for spermatazoa. P30 test (PSA) Prostatic Antigen. Only produced in the Prostate gland.
Disclaimer: These are MY notes taken from classroom lectures while I'm in the classroom. While I'm perfectly happy to share my notes with my classmates and I know I take very good notes, you should still make every effort to attend the class and TAKE YOUR OWN NOTES. I will not transcribe everything the instructor says in the classroom, and I will NEVER post pre-exam reviews. My notes will not replace the value of actually attending class and taking your own class notes.I also cannot attest to their accuracy, other than they are what was provided in the lecture; you should not reference my notes as "expert opionion" by any means, and if you notice an error or omission, please do me the favor of e-mailing me with the correction and I will re-post my notes. End of Disclaimer.