Unit 23: Forensic Evidence, Collection and Analysis
B: Investigate a simulated crime scene using forensic procedures
Investigating a crime scene
I am a trainee forensic technician working for the British Transport Police’s Scientific Support Unit (SSU). As part of
my training, my supervisor set up a simulated crime scene so that me and other trainees can act as crime scene
investigators (CSIs). I prepared appropriate documentation to record the crime scene and also collected, packaged
and labelled evidence to ensure it remains uncontaminated so that the continuity of evidence is maintained. This
task will help my supervisor decide if I am now competent to become an assistant CSI.
Initial assessment
The crime scene processing took place on Wednesday 24th May 2023 from 12:00 pm to 1:30 pm in room P105b at
Morpeth School. On arrival at the scene, we cordoned off the crime scene using barrier tape so that we could
preserve the crime scene and protect the evidence. This was done to ensure the integrity of evidence because using
police cordons only allows authorised personnel to enter the crime scene. If contamination was caused by an
individual outside of the authorised personnel, then this may lead to important evidence being damaged or
contaminated by mistake, which would leave the CSIs with less evidence to collect.
Many bloodstains of different patterns and sizes were present which straightaway suggested that violence must
have taken place and an individual was harmed. Harmful chemicals such as hydrochloric acid and nail varnish were
found to be spilt. Sharp objects such as scissors and a compass were spotted next to each other, possibly used to
harm the victim. A letter was found on one of the desks, which was written by the bank to the victim regarding
failed repayments for a mortgage.
A crime scene log was created so that we could keep track of who was responsible for certain duties at the crime
scene and what time they carried out their roles (see Appendix A1). This will help police officers to investigate a case
because each CSI would be held accountable for the responsibility that they had during crime scene processing.
Therefore, crime scene logs will help to maintain the integrity of evidence because only authorised personnel are
present at the scene, otherwise the crime scene could become contaminated if someone else outside of the
authorised personnel gains access to the site ie. to move any items. All evidence items present at the crime scene
were noted down in our crime scene notes before evidence collection (see Appendix A2). This was done so that the
crime scene can be documented in all states from start to end. Noting down the original state of the crime scene
was important in preserving the integrity of evidence because these notes could be used as written evidence of the
crime scene in the event that the photographs and/or evidence bags are lost.
Risk assessment
Before processing the crime scene, my team created a risk assessment for possible risks present at the crime scene
that may pose hazards when collecting evidence.
Carrying out a risk assessment before moving the evidence items was essential so that we could assess the risks
present at the scene so that health and safety measures could be put in place. This would prevent us from being
affected by certain hazards, such as being contaminated by the blood or HCl causing skin irritation. A risk assessment
was a crucial component to be carried out prior to our crime scene processing because certain hazards caused from
risks may result in contamination. For example, if a CSI tripped over the spilt hydrochloric acid or stepped in wet
bloodstains on the ground, this could cause the evidence in question to potentially smear or splash into other areas
of the crime scene. This would heavily affect a court case because the evidence contamination may lead CSIs to
,Unit 23: Forensic Evidence, Collection and Analysis
B: Investigate a simulated crime scene using forensic procedures
believe that a crime was carried out in a different way other than how it was originally carried out. Therefore,
incorrect suspicions of suspects would be made, leading to false prosecution and imprisonment.
Risk What hazards the risk can pose Size of risk Precautions
Blood Biohazard- Will have an effect on High Complete PPE must be worn
overall human health [1] when handling blood to avoid
contact and prevent risk of
infection
After collecting, hygienically
dispose of samples [1]
Hydrochloric acid Mild irritation to eyes, skin, High Avoid breathing in the gas
solution clothing produced from concentrated
solutions [2]
Corrosive [2]
Irritant [2]
Broken glass from Small fragments can be transferred Moderate Wear protective foot covers
nail varnish bottle to the clothing, hair or footwear of to prevent stepping in glass
anyone who handles the glass [3]
Full PPE (personal protective equipment) was worn to prevent contamination to the crime scene and to avoid being
exposed to hazardous substances. This included a jumpsuit, face mask, latex gloves and protective shoe covers.
Images of PPE worn throughout the investigation
Figure 1: PC 944HT wearing PPE
Figure 2: PPE jumpsuit worn
, Unit 23: Forensic Evidence, Collection and Analysis
B: Investigate a simulated crime scene using forensic procedures
Methods used to collect evidence
Blood and saliva
We used swabbing to collect blood. For most of the blood evidence, we picked up the sample with a cotton bud. For
bloodstains that had dried up, we added a small amount of distilled water to the cotton swab to moisten it and then
picked up a small amount of blood. Swabbing can be used to collect biological evidence such as blood, saliva,
semen, hair, etc. This is done by rotating a sterile cotton swab in the sample area and storing the swab in a small
plastic or glass vial. It is important to ensure that the swab is sterile when performing tests on the sample; this is so
that contamination can be avoided. After collecting each blood sample, we carried out the Kastle-Meyer test.
We used the Kastle-Meyer test to test for the presence of blood because it is an inexpensive process that can be
done in forensics. It is a reliable and quick method to test for blood and this was suitable for us to process our crime
scene because everything had to be done quickly. Furthermore, the Kastle-Meyer test can help to ensure the
integrity of the evidence. This is because CSIs will be able to come to a conclusion about each individual blood
splatter so that they can determine whether a sample is most likely to be blood; a positive result would indicate that
haemoglobin, a component of the blood, is present.
To carry this out, I used a cotton swab to collect a blood sample, ensuring to fully rotate it once so that enough
blood could be collected. I applied a drop of hydrogen peroxide solution and a drop of phenolphthalein to the cotton
swab. If the sample tested positive, the swab would turn pink. If the sample tested negative, the swab would
maintain its red colour or turn slightly black. We then recorded the results of the Kastle-Meyer test on a sheet of
paper (see Appendix A4). Swabbing was also used to collect saliva which was present on the glass of water (see
Appendix B5), this was also done by using a cotton swab to take a small sample of the saliva. Once I collected a
sample, I stored and labelled it in a plastic vial and this vial was placed into an evidence bag. All vials from the crime
scene were labelled with who handled the evidence, the crime incident number, time of evidence collection, date of
evidence collection and a description of the vial’s contents. We did not place each swab into an evidence bag
straightaway because this would cause the evidence on the swab to transfer onto the inside of the bag, which would
cause contamination.
We used cotton swabs to extract biological evidence from the crime scene because if the DNA was only placed in a
plastic bag (such as blood or other bodily fluids), then it could potentially leak from the bag. It is important to ensure
that the swab is sterile before use so that the sample is free from any contaminants that may produce a false result
when being tested in a laboratory for analysis, therefore reducing the integrity of the sample. A false sample may be
questioned in court and could cause forensic scientists to conclude that the biological evidence belongs to someone
