CRIMINALISTICS DNA & SEROLOGY

11/12/25

serology

identification of blood & bodily fluids at a crime scene

how does blood exams help the investigation?

locating the crime, discovering the crime, identifying the weapon, proving/disproving alibi & eliminating suspects

information available from blood testing tell whether visible stains

do or don’t contain blood

information available from blood testing tell whether blood is of 

human or non-human 

what does blood testing tell you?

age of the stain, if it’s human or not and blood group  

what can’t be identified through a blood exam

age & race

investigators must not overlook what three things of blood spatters, which may be useful for interpreting and reconstructing events that must have occured to cause the bleeding 

location, distribution and appearance 

kaster meyer color test 

chemicals put on a cotton swab to detect blood, if it turns bright pink then there was blood 

luminol test

a spray that shows invisible traces of blood under a luminescent light

precipitin

determines if it’s animal or human blood

rules for collecting and identifying blood on garments and fabrics 

investigators identify marks, garment must be completely dry, air dried at room temp, place in coldest/driest facility

how do you collect blood on solid surfaces 

scraped off and placed in airtight container 

how do you collect from glass 

submitted in small amounts so it can be insulated and the container must be marked 

how do you collect from dirt/sand 

collect in an air tight container 

how do you collect from liquid

collect at least 5³ cm in a container from the victim & suspect

what is a buccal swab 

a sterile tool to swab the cheeks/mouth for DNA 

what do the outer layer of skin cells do 

DNA bearing cells that are rubbed onto objects retrieved from crime scenes 

what do molecules do 

carry out the body’s genetic info 

CODIS

contains records of criminals/crime in all 50 states so you can compare DNA to their records

how is DNA collected

photograph it, clothes are put in paper bags/box to avoid fungi, dried blood uses a sterile cottonswab, biological evidence is refrigerated, standard is collected by swabbing mouth

how would a person gather DNA from a missing person 

by going in their bathroom and collecting DNA from their toothbrush or hairbrush

whats important to the interpretations of blood patterns

it helps detectives construct events of how the crime happened if they analyze the surface tension & direction of travel

how would you collect DNA that was left in a ransome note

photograph, wear latex gloves and swab the licked part of the envelope

what does DNA instruct your body to do 

make proteins