Fingerprint Examination Flashcards
Can you explain what the brush and powder method is and how it is used?
Brush and powder is a method for developing fingerprints, most often used at crime scenes.
The powder is applied to a feathered brush, and then lightly dusted over the surface being examined for fingerprints. The powder attaches to the fingerprint residue, therefore increasing the contrast between the fingerprint and its background.
This makes it easier to locate and preserve fingerprints at the crime scene.
The brush and powder method sounds like an abrasive method - how do you avoid damaging the fingerprint?
Fingerprints are fragile, and therefore surfaces are dusted for fingerprints using a circular motion, ensuring that only the very ends of the feathers make contact with the surface. This ensures that powder is applied to the surface without damaging the fingerprint.
What are fingerprint lifts?
Fingerprint lifts are square sheets of gelatine, with one side that is slightly tacky. When placed on a surface that has been dusted for fingerprints, the powder which has attached itself to the fingerprint is lifted from the surface by the gelatine.
The fingerprint lift is then placed tacky-side down on a square acetate sheet, along with a signed and dated label, which includes a unique identifier and a description of where the fingerprint was located.
Why were some of the exhibits examined at the scene, and others in the laboratory?
When we locate items at a crime scene, we make a judgement call as to whether that item would be better examined at the crime scene, or in the fingerprint lab where we have a greater number of treatments available to us.
This judgement is based on whether it is practical to remove and transport that item to the lab, and whether the results that we would achieve in the lab would likely be better than what can be achieved at the crime scene.
It is my opinion that examining the seized items in the lab would produce better results than what could be achieved at the crime scene, which is why they were removed from the vehicle for later examination in the lab.
I decided to examine the mobile phone at the scene as many of the treatments that are available in the fingerprint lab would compromise other types of forensic evidence, including the digital information held on the mobile phone. I therefore made the decision to use sterile brush and powder to examine the phone at the scene so that the other types of forensic evidence would be preserved.
What is superglue fuming, and how is this process used?
Superglue fuming is a method for developing fingerprints commonly used in the laboratory.
To superglue an item, the item is placed into a sealed chamber along with a small amount of superglue. When heated, the glue forms a vapour that fills the chamber.
Fingerprints attract the vapour which gradually forms a white layer of hardened glue. This layer not only makes the fingerprint more visible but also slightly more durable.
What is panacryl?
Panacryl is a dye stain that we use for enhancing fingerprints that have been developed using superglue fuming.
Fingerprints that have been treated with panacryl can be further enhanced using a forensic light source.
Are there other methods you could have used to develop fingerprints on this surface?
We have a range of methods available to us for developing fingerprints, and how we select a particular method depends on the constituents of the fingerprint, as well as the characteristics of the surface on which the fingerprint is deposited.
Based on my knowledge, training, and experience, the method that I selected was most appropriate for developing fingerprints on this type of surface.
What is RTX?
RTX, or ruthenium tetroxide, is a fuming method for developing latent fingerprints.
When examining an area for fingerprints with RTX, we use a handheld fumer, which vaporizes the RTX solution and produces a fume that can be directed toward a certain area with a small hose.
The RTX reacts with any fingerprints and turns them dark brown, therefore increasing the contrast between the fingerprint and the background surface, and making it easier to locate and preserve any fingerprints.
What measures were put in place to protect the integrity of the scene?
Throughout my examination of the vehicle, I wore full personal protective equipment to avoid contaminating the vehicle with my own fingerprints and DNA. This included a disposable suit, gloves, hair net, and mask.
Prior to beginning my examination, I had a discussion with members of ESR to determine what areas they would be interested in sampling for DNA. These areas, which included the interior door handles, were examined with a sterile brush and powder so that any fingerprints on these areas could be located and preserved before being sampled for DNA.
How do we know that the fingerprints you identified were the same fingerprints that were located at the scene?
I took photographs showing the location of all fingerprint lifts in situ prior to removing them from the vehicle. Each of these lifts were assigned a unique identifier which is visible in these photos, and once removed from the vehicle, these fingerprint lifts were given a signed and dated label that described the location of the fingerprint.
Following my examination of the vehicle, I hand-delivered all fingerprint lifts to the South Island Forensic Fingerprint Section for further examination.
Why did you examine these areas of the vehicle and not others?
Based on the information that I received about the offence prior to attending the scene, as well as discussions that I had with the Officer in Charge of the scene, I focused my examination on areas that were relevant given the circumstances of the offence.
Were any items seized from the vehicle?
Three items were seized from the vehicle, including a piece of brown tape from the rear passenger’s-side seat, a McDonalds cup from the front passenger’s seat, and a magazine clipping from the rear driver’s-side seat.
These items were photographed in situ before being removed from the vehicle and packaged.
What methods did you use to locate and develop fingerprints on the piece of tape?
I first used a forensic light source to examine the tape for fingerprints. Fingerprints were located but I was unable to successfully photograph them due to a lack of contrast between the fingerprint and the background surface.
The tape was then superglue fumed, and again visually examined with the forensic light source. The fingerprints that I had initially located appeared to be enhanced by the supergluing process. I labelled these fingerprints ‘A’, and preserved them with photography.
I then used panacryl to treat the non-sticky-side of the tape for fingerprints, and wet wop to treat the sticky-side of the tape for fingerprints. As a result of these treatments, I located two further fingerprints: one on the sticky-side of the tape, which I labelled ‘B’, and one on the non-sticky side, which I labelled ‘C’. Both fingerprints were preserved with photography.
What is the DCS5?
The DCS5 is a system that combines photography with specially designed computer software that assists us in locating and preserving fingerprints in the fingerprint lab.
What is a forensic light source?
A forensic light source is a specialised torch which is used to assist us in locating and preserving fingerprints both at the crime scene and in the fingerprint laboratory. The forensic light source emits high-intensity light in a range of different colours of light, and the specific colour of light used depends on the residue of the fingerprint, or the chemical used to enhance the fingerprint.
For example, we often use a chemical called panacryl, which is a dye stain that can be used for enhancing fingerprints. We can further enhance fingerprints developed using panacryl with a forensic light source emitting blue light.
