Biological Evidence

What is the importance of body fluids?

• provides key evidence in a criminal investigation and may assist the court in reaching conclusions

• establishes a link between identifying the fluid or tissue and the DNA profile, adds further weight to this evidence

What are the key values of biological fluids?

body fluid identification can:

• support activity-level information in cases

• assign relevance to DNA profiles resulting from stains

• elucidate even timelines

• support scene reconstruction

What are the purposes for locating biologcial forensic evidence?

• to find traces related to the alleged crime which can then be collected and from which the identity of the perpetrator may be revealed by further testing

• to contextualize the traces to provide information about what activities may have taken place

• to assess the cellular content of the primary stain to the DNA recovered from the evidentiary sample as some fluids have very high cellular content

• to assess whether the body fluid involved is likely to occur in what is suggested to be the primary location

What are the activity-level evaluations or contextualizing the scene?

1. Type of bodily fluid or organ tissue

2. Pattern of bodily fluid or organ tissue

3. Location of bodily fluid or organ tissue

4. Amount of bodily fluid or organ tissue

What is the debate on body fluids in court?

cases come to court in which the presence of cellular material of a person is not disputed but the activity that cause the deposition is

What are the activity-level evaluations?

weigh the likelihood of forensic evidence under:

• scenario 1 (H1, aka prosecution scenario)

• scenario 2 (H2, aka defense scenario)

H1 - Prosecution Scenario

the findings in the case can relate to the cellular material matching the victim or suspect which under H1 is indicative of an offensive activity

H2 - Defense Scenario

Questions cellular material on the evidentiary item:

• the cellular material was deposited not during the offence but at an earlier or later time

• the cellular material was not deposited by direct contact but the result of secondary (or tertiary, etc.) transfer

• the item on which the cellular material was deposited belongs to the suspect but was used in the offence by another person

• the cellular material was deposited on the knife in a different way

What is Luminol?

a reagent that is used to detect hemoglobin resulting in a blue fluorescence

What are the disadvantages of chemical sprays for blood?

• the luminescence produced can be short-lived

• in the case of luminal the visualization must be carried out in near darkness

What is the International Association of Bloodstain Pattern Analysts?

an organization of forensic experts specializing in the science of bloodstain pattern analysis

What can blood pattern analysis provide?

• direction of a droplet

• angle of impact

• type of wound

• distance from source

• force of nature

• relationship of victim to suspect

• number of blows struck

• nature of object

• direction of the force

• sequence of events

• which hand was used

What are the challenges of of BPA?

accuracy and reproducibility of conclusions by forensic bloodstain pattern analysts

What are the methods used by CFS for identification of bodily fluids and/or DNA testing?

• Kastly-Meyer (KM) Test

• ABAcard HemeTrace Test

• Phadebas Press test

What is the Kastle-Meyer (KM) Test?

a three-stage biochemical test that produces a pink colour reaction in the presence of either human or animal blood, as well as a number of other substances which do not appear blood-like

What is the ABAcard HemaTrace Test?

An immunological test that can be used to confirm that blood detected using the KM test is of human origin

What is the Phadebas Press Test?

used to localize possible saliva stains on items, through the detection of amylase - a protein often found in high levels of saliva but also feces, perspiration, vaginal secretions, and semen

What are the challenges of body fluids?

• lack of sensitivity or selectivity of some methods

• scene vs. lab uses

• only a single body fluid at a time can be measured

• methods may be destructive - DNA compromised

What are the challenges of DNA evidence-transfer?

the concepts of primary, secondary, and tertiary DNA transfer have been widely reported in scientific journals and revealed in cases of wrongful conviction

What are the relations to DNA evidence and stability?

• persistence and stability of DNA on various surfaces

• environmental factors degrade DNA

• degraded DNA is an issue

• properly stored DNA will last a long time

What are the challenges for DNA evidence stability?

• the STR regions of the DNA molecule can be fractured

• if STRs do not stay intact, amplification of these regions will not be successful

• the degradation can be identified because of the peak heights exhibiting a downward slope across the electropherogram

• reduced peak heights create a partial profile

What are the relation between DNA evidence and mixtures?

• DNA mixture (2 or more profiles)

• mixed DNA profile can be run against a suspect DNA (reference) to help identify them

• the mixed profile can be compared to another mixed profile

• mixed and partial profiles are challenges with DNA database

What is the DNA database?

CODIS

• regulated DNA federal database that mandates sample to be be specifically processed

What are the challenges with CODIS?

• may take several days to get results

• profile may not be in the database

What are the advantages of DNA profiling?

• linking crimes together where there are no suspects

• helping identify suspects

• eliminating suspects where there is no match between a crime scene DNA profile and a convicted offender’s DNA profile

• determining if a serial offender is involved

• identifying a victim

• identifying human remains

• assisting investigators, coroners, and medical examiners to find missing persons

What is the DNA profiling database in Canada?

National DNA Data Bank (NDDB)

What is the most common type of biological sample collected?

• 98.6% blood

• 1.3% buccal

• 0.1% hair

Is it possible to do DNA profiling at the police station?

Rapid DNA Act of 2017 allows DNA profiles to be generate outside accredited labs to be used to search CODIS

How does DNA profiling at the police station work?

• Buccal swab

• profile is then sent to the FBI’s CODIS database