investigation, as well as, crime scene processing. I will define what a crime scene is,
what makes it a crime scene and what happens at a crime scene. I will also explore what to
look for at a crime scene and what evidence will aid in the prosecutions of criminals.
Crime scene investigations can be indispensable in prosecuting a case, due the possibility
that mistakes can be made with forensics. Crime scene investigations include, but by no means
are limited to homicides, sexual assaults, armed robberies, home invasions and burglaries. There
is a lot of time spent processing crime scenes, packaging and transporting evidence,
attending and photographing autopsies. In criminal cases, this involves obtaining samples
from the crime-scene and a suspect, extracting the DNA, fingerprinting, weapons analysis,
and blood spatter analysis.
Forensic scientists compare DNA profiles to determine whether the suspect's sample
matches the evidence sample. A marker by itself, is not usually unique to an individual.
However, if two DNA samples are alike, odds are almost indisputable that the samples
are from the same person. If the sample profiles don't match, the person did not
contribute the DNA at the crime scene. If the patterns match, the suspect may have
contributed the evidence sample. While there is a chance that someone else has the same
DNA profile for a particular probe set, the odds are extraordinarily slim. In fact the overall
profile frequency is 0.00014 or about 1/7000. Therefore, a summary of the evidence is that
either the suspect contributed the evidence, or an unlikely coincidence happened. The once-in-
7000 coincidence that an unrelated person would by chance has the same DNA profile as that
obtained from uncorrupted evidence is rare enough to be almost incontrovertible.
The question is, how small do the odds have to be when conviction of the guilty or
acquittal of the innocent lies in the balance? Many judges consider this a matter for a
jury to take into consideration along with other evidence in the case. Experts point out
that using DNA forensic technology is far superior to eyewitness accounts, where the
odds for correct identification are about 50:50. Since blood evidence associated with a
crime can provide information that may solve the case, it is essential to correctly
document, collect, and preserve this type of evidence.
Improperly handled blood evidence can weaken or destroy a potential source of
facts in a case. Properly collected and preserved blood evidence can establish a strong
link between an individual and a criminal act. Blood evidence or the lack of blood
evidence can also be used to bolster or contradict a witness statement or any statements
that the suspect may make. Blood evidence can also point the investigator in the
direction he or she needs to go to solve the case. If blood evidence is documented,
collected, and stored properly, it can be presented to a judge or jury several years from
the time of the criminal act. Perhaps the most powerful application of blood evidence is
the ability to absolutely eliminate a person as a potential suspect in a crime.
The next obstacle at hand would be fingerprinting the crime scene and suspects. At
the time when fingerprint evidence was first admitted by courts, such evidence or
experience in dealing with millions of fingerprint records was not available. However, with the
data that is available today, it would be ludicrous to argue that the premises underlying
fingerprint identification have not been scientifically validated due to the accumulated experience
of the millions of fingerprints that have been scrutinized by experts. But, there is presently an