In this video, we shall learn about collecting of evidence from a crime scene with the help of mock.
How to collect evidence from crime scene?
In collecting evidence from a crime scene, the CSI has several main goals in mind: Reconstruct the crime, identify the person who did it, preserve the evidence for analysis and collect it in a way that will make it stand up in court.
Trace evidence might include gun-shot residue (GSR), paint residue, chemicals, glass and illicit drugs. To collect trace evidence, a CSI might use tweezers, plastic containers with lids, a filtered vacuum device and a knife. He will also have a biohazard kit on hand containing disposable latex gloves, booties, face mask and gown and a biohazard waste bag.
If the crime involves a gun, the CSI will collect clothing from the victim and anyone who may have been at the scene so the lab can test for GSR. GSR on the victim can indicate a close shot, and GSR on anyone else can indicate a suspect. The CSI places all clothing in sealed paper bags for transport to the lab. If he finds any illicit drugs or unknown powders at the scene, he can collect them using a knife and then seal each sample in a separate, sterile container. The lab can identify the substance, determine its purity and see what else is in the sample in trace amounts. These tests might determine drug possession, drug tampering or whether the composition could have killed or incapacitated a victim.
Technicians discover a lot of the trace evidence for a crime in the lab when they shake out bedding, clothing, towels, couch cushions and other items found at the scene. At the CBI Denver Crime Lab, technicians shake out the items in a sterile room, onto a large, white slab covered with paper.
The technicians then send any trace evidence they find to the appropriate department. In the Denver Crime Lab, things like soil, glass and paint stay in the trace-evidence lab, illicit drugs and unknown substances go to the chemistry lab, and hair goes to the DNA lab.
Body fluids found at a crime scene might include blood, saliva, and vomit. To identify and collect these pieces of evidence, a CSI might use smear slides, a scalpel, tweezers, scissors, sterile cloth squares, a UV light, protective eyewear and luminol. He’ll also use a blood collection kit to get samples from any suspects or from a living victim to use for comparison.
If the victim is dead and there is blood on the body, the CSI collects a blood sample either by submitting a piece of clothing or by using a sterile cloth square and a small amount of distilled water to remove some blood from the body. Blood or saliva collected from the body may belong to someone else, and the lab will perform DNA analysis so the sample can be used later to compare to blood or saliva taken from a suspect. The CSI will also scrape the victim’s nails for skin — if there was a struggle, the suspect’s skin (and therefore DNA) may be under the victim’s nails. If there is dried blood on any furniture at the scene, the CSI will try to send the entire piece of furniture to the lab. A couch is not an uncommon piece of evidence to collect. If the blood is on something that can’t reasonably go to the lab, like a wall or a bathtub, the CSI can collect it by scraping it into a sterile container using a scalpel. The CSI may also use luminol and a portable UV light to reveal blood that has been washed off a surface.
If there is blood at the scene, there may also be blood spatter patterns. These patterns can reveal the type of weapon that was used — for instance, a “cast-off pattern” is left when something like a baseball bat contacts a blood source and then swings back. The droplets are large and often tear-drop shaped. This type of pattern can indicate multiple blows from a blunt object, because the first blow typically does not contact any blood. A “high-energy pattern,” on the other hand, is made up of many tiny droplets and may indicate a gun shot. Blood spatter analysis can indicate which direction the blood came from and how many separate incidents created the pattern. Analyzing a blood pattern involves studying the size and shape of the stain, the shape and size of the blood droplets and the concentration of the droplets within the pattern. The CSI takes pictures of the pattern and may call in a blood-spatter specialist to analyze it.
Hair and Fibers
A CSI may use combs, tweezers, containers and a filtered vacuum device to collect any hair or fibers at the scene. In a case of with a live victim, the CSI accompanies the victim to the hospital to obtain any hairs or fibers found on the victim’s body during the medical examination. The CSI seals any hair or fiber evidence in separate containers for transport to the lab.
A CSI might recover carpet fibers from a suspect’s shoes. The lab can compare these fibers to carpet fibers from the victim’s home.