Crime Scene Investigation: Introduction
Lesson Objectives:
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What is Physical Evidence?
Physical evidence encompasses any and all objects that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator.
Common Types of Physical Evidence
1. Blood, semen and saliva – used to determine identity and possible origin
2. Documents
3. Drugs
4. Explosives
5. Fibres
6. Fingerprints
7. Firearms and ammunition
8. Glass
9. Hair
10. Impressions – includes tyre marks, shoe prints etc
11. Organs and physiological fluids – to detect drugs and/or poisons
12. Paint
13. Petroleum products – e.g. petrol residues removed from the scene of an arson
14. Plastic bags
15. Powder residues – i.e. firearm discharge residues
16. Serial numbers – restoration of erased serial numbers from stolen items
17. Soil
18. Tool marks
19. Vehicle lights
20. Wood and other vegetative matter – can link a person to a crime location
At a crime scene physical evidence is collected and preserved for examination. A crime scene examiner must be able to recognise and preserve physical evidence.
Objectives of Crime Scene Examination:
· Gather samples
· Investigate crime
· Recover anything of potential value
· Collect anything that may test the theory as to what happened
· Better to collect too much than too little
· May not have access to scene later on, therefore enough of each sample must be collected first time
There are 6 steps involved in crime scene examination:
Step 1:
Identify and secure the crime scene:
· Clear unauthorised persons – SOCO’s, Senior Garda investigator, Pathologist, Forensic Scientist, Fire Investigator allowed at scene
· Get medical attention if required
· Protect and preserve the scene- crime scene tape, tent if outdoors
· Identify entry and exit points
Step 2:
Record the crime scene
· Must be recorded in untouched state
· Photography – overall and up close, use ruler for scale
· Sketch - Rough sketch done at scene included accurate measurements of distance. Smooth sketch done at later date includes compass, scale and legend.
· Notes:
- Should be detailed
- Time, date
- Lighting conditions
- Weather, temperature
- Describe scene
- Who is at scene
- Entry and exit points
- Location
- Condition of location
- Signs of forced entry
- Condition of the body
- Unusual sounds/smells
· Passive Documentation – no interpretation just facts about crime scene
· Active Documentation – includes recognition of valuable evidence and interpretation of the evidence if possible
Step 3:
Search for evidence
· All persons entering crime scene must use common approach path – preferably a different path than the one that the perpetrator used.
· In case of murder, the body and its immediate area should be searched first. Once the body moved underneath can be searched. The head, hands and feet should be bagged and the body placed in body bag. The body is then removed via the common approach path.
· Searching the scene should be systematic – Spiral or wheel for small scenes. Grid, line or quadrant for larger scenes.
· Evidence can be large or microscopic.
· Crime scene examiners wear plastic disposable overalls, gloves etc – protect wearer and protect crime scene from contamination
· If more than one scene it is best practice for different crime scene examiners to process scenes, if not possible the crime scene examiner must change overalls etc to prevent cross-contamination of evidence.
Step 4:
Collect and package the evidence
· What to collect?
· Anything that is unusual in that environment
· Anything that is in an unusual position
· Anything that is in an unusual condition
· Control Samples – physical evidence whose origin is known e.g. blood or hair from a suspect, that can be compared to crime scene evidence
· Packaging of the evidence correctly is very important. Correct packaging ensures the integrity of the samples by
· Preventing damage
· Preventing loss
· Preventing contamination – victim and suspects clothing etc should not be packaged together
· Demonstrates the integrity by keeping the item sealed – to show the item has not been tampered with
· When working with very small samples it is important to show that the evidence is connected to the crime and not as a result of contamination
· Packaging of commonly occurring samples
· Arson accelerants – liquid samples should be contained in glass bottles, clothing should be stored in nylon bags. Plastic will affect samples as the accelerant can react with it. Accelerants can pass through polystyrene bags. Nylon impermeable to most liquids.
· Body fluids – Liquids should be contained in glass or plastic bottles and stored frozen. Stained items of clothing should be air dried at room temperature if wet then stored in paper bags and sealed. Control blood samples should be stored in plastic tube with anti-coagulant. Swabs stored frozen between collection and analysis.
· Small samples e.g. paint and glass – small plastic tubes or self-seal envelopes
· Tools or weapons – special plastic tubes that are adjustable in length
· Tape lifts – used to remove trace evidence from surfaces rather than remove whole item from crime scene.
· Tamper evident bags – each bag has an individual serial number, therefore are easy to track. Cannot reopen at seal. The bag is open at area away from the seal and the bag is signed showing who has opened the bag and the seal hasn’t been tampered with.
· Labelling of items gives each sample a unique identity.
Step 5:
Maintain chain of custody
· Everybody that handles evidence must be accounted for – it is easy for samples to be mixed up / contaminated, therefore a very strict record must be kept from the moment the samples are collected to the moment it arrives in court
· The evidence will be inadmissible in court if there are gaps in the record.
· The forensic scientist will initial and date each item examined to give it an identifying mark when the item is brought to court.
Step 6:
Submit Evidence
An evidence submission form accompanies the evidence. This includes the following information – type and date of crime, what’s in the package and what examinations are required.
Crime Scene Reconstruction
Reconstructing a crime scene involves a collaborative effort between crime scene examiners, forensic scientists and the detectives investigating the crime. The physical evidence gathered at a crime scene can support or contradict the accounts given by witnesses and/or suspects. The accurate documentation of the crime scene is a very important part of reconstruction. Reconstruction generally takes place at a later stage following the crime scene examination and therefore relies on the photographs, notes and sketches taken at the scene.
Reconstruction supports a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by witnesses and those involved with the incident.
Examples of crime scene reconstruction:
- Using lasers or rods to plot approximate bullet trajectory can help predict the position of the shooter relative to the victim.
- Blood spatter analysis can tell the direction of impact, give information on the type of weapon used and estimate the number of blows given by the perpetrator to the victim.
- Direction of impact for projectiles penetrating glass objects.
- Gunshot residue on victims clothing can indicate the distance of a shooter from the victim.
When you have completed the lesson click here to solve a crime!!
Interactive Games, Click here
What is Physical Evidence?
Physical evidence encompasses any and all objects that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator.
Common Types of Physical Evidence
1. Blood, semen and saliva – used to determine identity and possible origin
2. Documents
3. Drugs
4. Explosives
5. Fibres
6. Fingerprints
7. Firearms and ammunition
8. Glass
9. Hair
10. Impressions – includes tyre marks, shoe prints etc
11. Organs and physiological fluids – to detect drugs and/or poisons
12. Paint
13. Petroleum products – e.g. petrol residues removed from the scene of an arson
14. Plastic bags
15. Powder residues – i.e. firearm discharge residues
16. Serial numbers – restoration of erased serial numbers from stolen items
17. Soil
18. Tool marks
19. Vehicle lights
20. Wood and other vegetative matter – can link a person to a crime location
At a crime scene physical evidence is collected and preserved for examination. A crime scene examiner must be able to recognise and preserve physical evidence.
Objectives of Crime Scene Examination:
· Gather samples
· Investigate crime
· Recover anything of potential value
· Collect anything that may test the theory as to what happened
· Better to collect too much than too little
· May not have access to scene later on, therefore enough of each sample must be collected first time
There are 6 steps involved in crime scene examination:
Step 1:
Identify and secure the crime scene:
· Clear unauthorised persons – SOCO’s, Senior Garda investigator, Pathologist, Forensic Scientist, Fire Investigator allowed at scene
· Get medical attention if required
· Protect and preserve the scene- crime scene tape, tent if outdoors
· Identify entry and exit points
Step 2:
Record the crime scene
· Must be recorded in untouched state
· Photography – overall and up close, use ruler for scale
· Sketch - Rough sketch done at scene included accurate measurements of distance. Smooth sketch done at later date includes compass, scale and legend.
· Notes:
- Should be detailed
- Time, date
- Lighting conditions
- Weather, temperature
- Describe scene
- Who is at scene
- Entry and exit points
- Location
- Condition of location
- Signs of forced entry
- Condition of the body
- Unusual sounds/smells
· Passive Documentation – no interpretation just facts about crime scene
· Active Documentation – includes recognition of valuable evidence and interpretation of the evidence if possible
Step 3:
Search for evidence
· All persons entering crime scene must use common approach path – preferably a different path than the one that the perpetrator used.
· In case of murder, the body and its immediate area should be searched first. Once the body moved underneath can be searched. The head, hands and feet should be bagged and the body placed in body bag. The body is then removed via the common approach path.
· Searching the scene should be systematic – Spiral or wheel for small scenes. Grid, line or quadrant for larger scenes.
· Evidence can be large or microscopic.
· Crime scene examiners wear plastic disposable overalls, gloves etc – protect wearer and protect crime scene from contamination
· If more than one scene it is best practice for different crime scene examiners to process scenes, if not possible the crime scene examiner must change overalls etc to prevent cross-contamination of evidence.
Step 4:
Collect and package the evidence
· What to collect?
· Anything that is unusual in that environment
· Anything that is in an unusual position
· Anything that is in an unusual condition
· Control Samples – physical evidence whose origin is known e.g. blood or hair from a suspect, that can be compared to crime scene evidence
· Packaging of the evidence correctly is very important. Correct packaging ensures the integrity of the samples by
· Preventing damage
· Preventing loss
· Preventing contamination – victim and suspects clothing etc should not be packaged together
· Demonstrates the integrity by keeping the item sealed – to show the item has not been tampered with
· When working with very small samples it is important to show that the evidence is connected to the crime and not as a result of contamination
· Packaging of commonly occurring samples
· Arson accelerants – liquid samples should be contained in glass bottles, clothing should be stored in nylon bags. Plastic will affect samples as the accelerant can react with it. Accelerants can pass through polystyrene bags. Nylon impermeable to most liquids.
· Body fluids – Liquids should be contained in glass or plastic bottles and stored frozen. Stained items of clothing should be air dried at room temperature if wet then stored in paper bags and sealed. Control blood samples should be stored in plastic tube with anti-coagulant. Swabs stored frozen between collection and analysis.
· Small samples e.g. paint and glass – small plastic tubes or self-seal envelopes
· Tools or weapons – special plastic tubes that are adjustable in length
· Tape lifts – used to remove trace evidence from surfaces rather than remove whole item from crime scene.
· Tamper evident bags – each bag has an individual serial number, therefore are easy to track. Cannot reopen at seal. The bag is open at area away from the seal and the bag is signed showing who has opened the bag and the seal hasn’t been tampered with.
· Labelling of items gives each sample a unique identity.
Step 5:
Maintain chain of custody
· Everybody that handles evidence must be accounted for – it is easy for samples to be mixed up / contaminated, therefore a very strict record must be kept from the moment the samples are collected to the moment it arrives in court
· The evidence will be inadmissible in court if there are gaps in the record.
· The forensic scientist will initial and date each item examined to give it an identifying mark when the item is brought to court.
Step 6:
Submit Evidence
An evidence submission form accompanies the evidence. This includes the following information – type and date of crime, what’s in the package and what examinations are required.
Crime Scene Reconstruction
Reconstructing a crime scene involves a collaborative effort between crime scene examiners, forensic scientists and the detectives investigating the crime. The physical evidence gathered at a crime scene can support or contradict the accounts given by witnesses and/or suspects. The accurate documentation of the crime scene is a very important part of reconstruction. Reconstruction generally takes place at a later stage following the crime scene examination and therefore relies on the photographs, notes and sketches taken at the scene.
Reconstruction supports a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by witnesses and those involved with the incident.
Examples of crime scene reconstruction:
- Using lasers or rods to plot approximate bullet trajectory can help predict the position of the shooter relative to the victim.
- Blood spatter analysis can tell the direction of impact, give information on the type of weapon used and estimate the number of blows given by the perpetrator to the victim.
- Direction of impact for projectiles penetrating glass objects.
- Gunshot residue on victims clothing can indicate the distance of a shooter from the victim.
Interactive Crime Scene Investigation
An extremely valuable painting has been stolen from the Hangem Art Gallery.
The theft of the painting, by the well renowned artist Ivor B Rush, was reported by the security guard, Ken Locket, when he opened up the gallery at 7.30am this morning.
You are called to the scene and your investigation begins.
You establish the last person to see the painting was the cleaner, Dusty Shaker, who states she finished cleaning the gallery at 7.30pm the previous evening. At this time she insists the painting was hanging on the wall.
Three people have keys to the building they are Locket, Shaker and the caretaker Phil Mepocket. There is no sign of forced entry to the gallery.
You further establish Mepocket is on holiday this week and has not been at the art gallery since the previous week.
Examine the crime scene, gather the evidence and then process it in the laboratory. Be warned if you fail to do this correctly valuable information will be lost. If you need assistance you can ask our expert “the prof.
Good Luck in your Investigation! Click here to solve the crime
Three people have keys to the building they are Locket, Shaker and the caretaker Phil Mepocket. There is no sign of forced entry to the gallery.
You further establish Mepocket is on holiday this week and has not been at the art gallery since the previous week.
Examine the crime scene, gather the evidence and then process it in the laboratory. Be warned if you fail to do this correctly valuable information will be lost. If you need assistance you can ask our expert “the prof.
Good Luck in your Investigation! Click here to solve the crime
