forensics Flashcards
what is the definition of Locards Principle
every contact leaves a trace= trace evidence
what is the physical fit for a crime scene?
the connection between the crime scene and the suspect eg. car left paint and drove away. the paint traced back to the car
two ways to target potential traces?
1) reactive trace= automatic/ reflective behaviour triggered by stimuli, something associated with past experiences eg flinching when hearing a loud noise.
2) incentive trace= driven by anticipation for future awards and goal directed behaviour to receive a outcome
eg studying for an exam to get a good grade
methods of analysis for trace material ?
1) scanning electron microscope (SEM): analyses trace material such as soil, gunshot residue or metal frgaments
2) energy dispersive x ray spectroscopy (EDS): paired with SEM to analyse elemental composition of material.
fibre-
3) thin layer chromatography- identify chemical composition of dye eg matching clothing fibres
4) infrared spectroscopy-
each fibre eg (cotton, wool) has a unique infrared absorption spectrum to distinguish between different types of fibres.
preliminary tests of semen and saliva?
semen- (good source of DNA)
seminal fluid is sterile (no sperm)
1) acid phosphatase test (AP)-
an enzyme present in high concentrations of semen, however it can be found in other bodily fluids.
2) UV light/ microscopy
saliva-
main saliva test= amylase test-
enzyme found in saliva breaks down starch.
however saliva may contain bacterial/ cheek cells
the 4 different types of blood pattern?
1) passive= due to gravity eg. drips, drops, pools
2) transfer= wet bloody surface in contact with another surface produces a pattern eg handprint swipe/ smear.
3) impact and projected patterns= can occur at a low, medium or high velocity= arterial spurt/ gush by a weapon
the challenges of gathering reliable trace evidence?
1) contamination
2)evidence could come from a variety of sources
3) evidence could degrade
