There are several Forensic Techniques used by Police Officers and Investigators to investigate a crime:
1. Fingerprinting:
Every single person has a unique fingerprint. Even identical twins develop different fingerprint patterns inside the womb. Back in time, the system used to record people's identity used fingerprints. The process of fingerprinting is called dactyloscopy. A person's fingers are cleaned with alcohol to remove sweat and dried carefully. The person will roll his or her fingertips in ink to cover the whole fingerprint area. Then each finger is rolled from one end of the fingernail to another on a prepared sheet of paper to be rolled fingerprints. Flat impressions are made by applying one's fingers onto a sheet of paper. Flat impressions are used to verify rolled fingerprints.
Fingerprints have been used by law enforcement agencies for over a century.
1. Fingerprinting:
Every single person has a unique fingerprint. Even identical twins develop different fingerprint patterns inside the womb. Back in time, the system used to record people's identity used fingerprints. The process of fingerprinting is called dactyloscopy. A person's fingers are cleaned with alcohol to remove sweat and dried carefully. The person will roll his or her fingertips in ink to cover the whole fingerprint area. Then each finger is rolled from one end of the fingernail to another on a prepared sheet of paper to be rolled fingerprints. Flat impressions are made by applying one's fingers onto a sheet of paper. Flat impressions are used to verify rolled fingerprints.
Fingerprints have been used by law enforcement agencies for over a century.
![Picture](/uploads/5/9/5/6/59567625/7230322.jpg?186)
Nowadays they take picture of fingerprints with digital scanning technologies. This is done by applying one's fingers onto the reader surface and hold them for several seconds.
![Picture](/uploads/5/9/5/6/59567625/1762925.jpg?250)
There are two types of fingerprints that can be found at a crime scene. Visible and latent fingerprints. Visible fingerprints result in an impression on the surface of objects (clay, blood, dirt). Latent fingerprints are harder to detect and be collected to the lab. Investigators have different ways to collect fingerprints from a crime scene.
1. Black powder
By using a brush with black powder to brush over the place where the fingerprints are located. The black powder will stick to the body's natural oil and sweat and reveal the fingerprints.Finally, use a piece of clear adhesive tape to lift the DNA off.
However the fingerprint powder can contaminate valuable forensic evidences.
1. Black powder
By using a brush with black powder to brush over the place where the fingerprints are located. The black powder will stick to the body's natural oil and sweat and reveal the fingerprints.Finally, use a piece of clear adhesive tape to lift the DNA off.
However the fingerprint powder can contaminate valuable forensic evidences.
![Picture](/uploads/5/9/5/6/59567625/5924463.png?315)
2. Alternate Light Source (ALS)
Because of the disadvantage of using fingerprint powder, investigators usually use Alternate Light Source to detect the presence of fingerprints. By this, the sample is not ruined or any other evidence is not affected.
The ALS emits particular wavelengths of light and eventually shows the fingerprints.
A Forensic Light Source is made up of a lamp containing ultra-violet, visible and infrared components of light. By different light interaction techniques, the light source has different purpose. In the detection of fingerprint, fluorescence light technique is used.
ALS increases the types of surfaces from which a fingerprint can be detected.
Because of the disadvantage of using fingerprint powder, investigators usually use Alternate Light Source to detect the presence of fingerprints. By this, the sample is not ruined or any other evidence is not affected.
The ALS emits particular wavelengths of light and eventually shows the fingerprints.
A Forensic Light Source is made up of a lamp containing ultra-violet, visible and infrared components of light. By different light interaction techniques, the light source has different purpose. In the detection of fingerprint, fluorescence light technique is used.
ALS increases the types of surfaces from which a fingerprint can be detected.
![Picture](/uploads/5/9/5/6/59567625/5235276_orig.jpg)
3. Chemical, ninhydrin and physical developer:
Porous surface such as paper is process with chemical. The substance will react with amino acids, salts, some specific components of the latent fingerprint. Ninhydrin turns prints into purple which can easily be photographed.
Porous surface such as paper is process with chemical. The substance will react with amino acids, salts, some specific components of the latent fingerprint. Ninhydrin turns prints into purple which can easily be photographed.
![Picture](/uploads/5/9/5/6/59567625/9110304.png?568)
2. DNA
DNA, like fingerprint, is considered to be a person's unique trait. However, DNA is the same in identical twins.
DNA can be found in ALL cells of the body and they're almost the same in every single cell. (In particular cells, some parts of DNA is switched off so cell can have certain functions).
To know more about DNA and its application in forensic science, click here.
3. Ballistics/Gun shots:
The bullet can identify what type of gun a criminal used. Investigators study the markings which are called rifling impressions found on a bullet or the impact a bullet made on any surface can determine exactly which gun the bullet was fired from.
The barrel is a long tube that the bullet travels through before it exits the firearm. The barrel has many shallow ridges which creates impressions on the bullet to help it fly in a straight direction.
Each gun has an unique barrel which creates different pattern carved on the bullet's surface, resulting in a distinguished rifling impression. Once investigators have identified these markings, they can easily match the bullet to the correct gun.
![Picture](/uploads/5/9/5/6/59567625/2416987.png?567)
The bullet diameter - the caliber can also help to determine the type of gun the criminal was using as well.
![Picture](/uploads/5/9/5/6/59567625/1352812_orig.png)
Looking at a bullet, an investigator can tell the rifling number and the rifling direction of the cartridge.
The type of gun is determined by the bullet's caliber, type of rifling, rifling number and rifling direction.
3. Hairs and fibers
By collecting hairs and fibers at the crime scene, vitally important evidences can be picked up and used against the criminal.
There are two types of fibers, natural and synthetic fibers. Natural fibers can be hair, fur, wool, etc. Synthetic fibers can be polyester, acrylic, etc. Natural fibers appear to be coarse with overlapping scales. Synthetic fibers, on the other hand, are really smooth.
A famous crime back in the 1960 was solved by the study of hairs and fibers.
Graeme Thorne kidnapping - the first known kidnapping for ransom in Australian criminal history.
His parents won a lottery. The news about Mr and Mrs Thorne who had just won a huge amount of money spread everywhere. One day
3. Hairs and fibers
By collecting hairs and fibers at the crime scene, vitally important evidences can be picked up and used against the criminal.
There are two types of fibers, natural and synthetic fibers. Natural fibers can be hair, fur, wool, etc. Synthetic fibers can be polyester, acrylic, etc. Natural fibers appear to be coarse with overlapping scales. Synthetic fibers, on the other hand, are really smooth.
A famous crime back in the 1960 was solved by the study of hairs and fibers.
Graeme Thorne kidnapping - the first known kidnapping for ransom in Australian criminal history.
His parents won a lottery. The news about Mr and Mrs Thorne who had just won a huge amount of money spread everywhere. One day
Source: http://science.howstuffworks.com/fingerprinting2.htm
http://science.howstuffworks.com/enlarge-image.htm?terms=Fingerprint&page=3
http://www.forensicsciencesimplified.org/prints/how.html
http://www.horiba.com/fileadmin/uploads/Scientific/Documents/Forensics/fls.pdf
http://science.howstuffworks.com/fingerprinting.htm
http://www.crimemuseum.org/crime-library/ballistics
http://www.firearmsid.com/A_BulletId.htm
http://forensics.rice.edu/
http://www.forensicsciencesimplified.org/prints/how.html
http://www.horiba.com/fileadmin/uploads/Scientific/Documents/Forensics/fls.pdf
http://science.howstuffworks.com/fingerprinting.htm
http://www.crimemuseum.org/crime-library/ballistics
http://www.firearmsid.com/A_BulletId.htm
http://forensics.rice.edu/