What is positive identification?
- narrowed down to a single individual (cannot be anyone else)
- done by matching premortem to postmortem records
What methods are used to determine a positive ID?
- visual ID
- Fingerprints
- medical records
- x-rays
- DNA
- video superimposition
- dental records
- circumstantial
How is visual identification conducted and what problems exist with this method?
- done by family and friends who ID based on unique feature or marks
- body must be fresh
- tentative ID required first
problems: - distressing, denial is a common reaction, mistaken identity
What are the 3 fundamental principles of fingerprints?
- individualizing - no 2 fingers possess the same ridge characteristics
- unchangeable - does not change throughout life
- classifiable - ridge patterns can be systemically classified
How was fingerprint classification developed and what are the 3 common patterns?
Henry System was developed by Scotland Yard and computerized by FBI, which turned into the IAFIS
- common patterns = whorl, loop, arch
How is a fingerprint comparison conducted?
- compare unknown to known print
- if an incorrect ID is made, this is called a fatal mistake (officer will be suspended and required to regain certification)
What are the 3 levels of detail?
level 1 - pattern (whorl, loop, arch)
level 2 - minutiae (fine lines)
level 3 - pore and ridge shape
If a victim is highly decomposed how can fingerprints be recovered?
when the body decomposes, the skin sloughs off and investigators can actually put the sloughed skin of the human hand over a glove and fingerprint themselves thus recovering the victim’s prints
what are some problems with fingerprint ID and analyses?
- victim must have premortem record or prints will have to be retrieved from personal items
How can dental record be used for positive ID?
- if a body is skeletonized or highly decomposed, the teeth can be compared to the victim’s dental record (assuming they have one)
- antemortem record needed and tentative ID
How can medical records be used for positive ID?
- comparing antemortem to postmortem x-rays
- observing healed fractures or degenerative changes
- can also find implants: locate serial number which can lead you to the manufacturer, hospital, surgeon, and patient
- can also look at frontal sinuses (supposedly unique)
How can medical records determine positive ID?
- records are often detailed (depends on physician)
- notes about surgeries or scars
What is the difference between nuclear and mitochondrial DNA?
nuclear = 50% random mix from both parents (can get sample from parents/siblings) mitochondrial = maternal line only (can get premortem sample from mom)
Where are sources of DNA in a live person? dead person?
live: - blood, skin tissue, hair follicle dead: - fresh body = blood, tissue, hair root - decomposed/skeletonized = bone marrow, teeth (dentine)
What is done for DNA comparison?
- DNA from unknown body compared to sample from premortem record
- crime scene DNA is entered into CODIS
- gives profile NOT ID
What DNA gets entered into the DNA databank?
- offenders convicted of serious crimes
* DNA from investigation is NOT entered, they are destroyed
National DNA Databank of Canada
- crime scene index - samples from unsolved crimes
- convicted offenders’ index - samples from people who are incarcerated and convicted of sexual assault and murder
- missing persons index - DNA from missing persons and found human remains
What is video superimposition and who performs this?
- matching tentative ID photo with skull
- better for elimination than ID
- anthropologist and x-ray specialist
How can children be identified?
mostly through DNA from toys, mouth guards, or retainers
Why is identifying children so difficult?
- lack detailed medical records and dental records
- small bones that have not yet ossified (often lost)
- sex, and ancestry not identifiable in children
- stature changes quickly
