Types of Evidence Recovered

There are three main types of evidence that can be recovered from the scene of a crime, they are physical evidence, biological evidence and chemical evidence.

Physical evidence is any piece of material evidence that was used in a crime, this could range from anything from a gun to a piece of broken glass that was used to stab someone. Weapons are usually the first thing scenes of crime officers will look for during a murder case. It is very important that if a piece of evidence is found, it should be measured correctly and photographs should be taken. A murder weapon is an extremely important piece of evidence to find because it not only will tell us how the victim has died but it can also give us information about the killer. A lot of the time things like fingerprints and bodily fluids are found on murder weapons which can link people to the scene of the crime. Tools are very commonly used murder weapons, this may include screwdrivers, hammers and wrenches etc. As tools are used they can get chipped and scratched, this can be used to compare the evidence found with the suspect. The type of screwdriver can be easily confirmed by looking at the entry would of the victim. You can match the size and shape of the entry wound with the size and shape of the suspected screwdriver, these tools are also good for picking up traces of things like fingerprints and bodily fluids which can be sent back to the lab for testing. Clothing is a very commonly found piece of evidence, Just like the other pieces of physical evidence it is very important to note down all of the characteristics of the clothing. The clothing that is found would give the investigator some knowledge on what the criminal might look like, for example, if the shirt is a male shirt in a large size then he would know that he is after a tall male. Clothing is very good at absorbing bodily fluids such as blood, saliva and semen. This means that the item to be tested on and can provide the case with a lot of information about the suspect. There can also be slits in clothing when the victim has been stabbed, by measuring these slits, the forensic analyst can estimate the length and width of the blade or screwdriver.

Fingerprints, hair and bodily fluids are all pieces of biological evidence. This is evidence that comes from something that is living. Bodily fluids are very useful for forensic scientists due to the fluids having a cellular structure; this means that if nuclei are present then it will contain DNA which is used to identify criminals easily. Blood is a very good piece of evidence when trying to put someone at the scene of a crime. A person can be easily identified by their blood. Forensic scientists can tell a lot from just looking at blood, for example if the blood is bright red then you can expect it is fresh, if the blood is a brownish colour then you can tell that it has been left for a long time. Even if the criminal tries to clean up the blood it can still be identified as it strongly absorbs infrared. Everyone’s fingerprint patterns are formed in the early stages of pregnancy and they are also the last thing to decay when we die which is a good thing for a forensic scientist because if someone is suspected to have committed a crime dies, their prints will still be available for testing. Fingerprints are a very good piece of evidence to find at a crime as everyone’s fingerprints are different and have different characteristics, for example a fingerprint that is found at a crime scene could have a loop pattern whereas the main suspect may have a whorl pattern. Nevertheless, this does not mean they did not commit the crime, like other pieces of evidence, fingerprints mean very little on their own and need other pieces of evidence to support it. 

Chemical evidence can come in the form of a solid, liquid or a gas. Some solids would include gunshot residue and drugs, some liquids would include acids and poisons, some gases would include butane and propane. The most commonly found piece of chemical evidence would be gunshot residue. Gunshot residue can be found at near enough every case where a gun has been fired. When someone does pull the trigger on a gun a combustion reaction takes place which then results in gunpowder being released, this powder gets released backwards which means a lot of it will land on the forearm of the person who pulled the trigger and on the ground surrounding them. This gives the forensic analyst a good idea where the person was standing when they shot the gun and they can also do spot tests on the arms of the suspects for gunpowder. The reaction that takes place when a gun is fired is a heat releasing exothermic reaction which results in chemicals being thrown everywhere. A residue gets discharged every time the gun gets fired, to find these residues forensic scientists would carry out spot tests to see if anything was present. The second most commonly found piece of chemical evidence would be drugs, in which specialist equipment such as a spectrophotometer needs to be used.