Friction ridge impressions (fingerprints), may also have features that help the examiner narrow the search, by indicating which digit may have left the impression. This can be immensely useful when conducting a search, or when theorizing what a person may have been doing, when the impression was deposited. Ultimately, such theories are circumstantial information provided by the forensic investigation. But, at times, this information may corroborate or refute statements, as well as provide leads for the case.
The features of an impression, which may provide such insights, is the location, the orientation, and the flow of the friction ridges present. Here are some of the aspects to look for, when examining fingerprints.
Location and Orientation
Often key to determining contextual information about when the impression was deposited.
On closer examination, you can see the orientation of the impression is downwards.
Fingerprint located on the exterior of the drive side door. However it is located at the top of the door, above the window.
As you will learn, from digit determination information provided below, that this also appears to be an impression left by a finger, most likely from the right hand. As such, it was reasonable to believe this impression was left, when the door to the vehicle was open.
A large glass window broken to gain entry into a home, where multiple items are stolen.
But, a large collection of impressions located on the glass
The impressions were all identified to a person who was known to often be lawfully at the residence. So it may have been argued the impressions on the glass were left at a time when that person was lawfully present.
However, this window was a triple pane window, and some impressions were located on the middle pane of glass.
Therefore, it could be reasonably believed the impressions were left, after the glass was broken.
In addition to the location and orientation of an impression, which may provide unique contextual information, and aid in determine which digit (finger) left the impression. There are aspects of the friction ridges within, that may provide similar insights.
Pattern Type - and how it can help!
The most common pattern type is the loop pattern, estimated at ~60% of all fingerprints. However, the type of loop, may help indicate what hand it is on.
Loops are divided into two categories, Ulnar and Radial.
Ulnar (U) - the friction ridge flow is towards, and from the little finger side of the hand. Named after the Ulna bone in the forearm.
Radial (R) - the friction ridge flow is towards, and from the thumb side of the hand. Named after the radius bone in the forearm.
Now you cannot determine which type it is, until you know the hand. But, in many studies, which have examined millions of fingerprints. It has been found that over 90% of all loop pattern impressions, are ulnar loops.
As well, if the radial pattern existed, it is most commonly found on the forefinger (also referred to as the index or pointer finger).
So, for the two impressions seen here. You can see the friction ridges flow towards, and from, the right side. This provides an indication the impressions are likely from fingers on the right hand, or the left forefinger. Although this only narrows the search a little, it can be very helpful for examiners. As well as, provide insights into context based upon where the impression was found, and its orientation.
A similar insight can be provided by the tenter arch (T) pattern, as shown here.
The majority of tented arch patterns are found on the forefinger (index) as well (over 50%). But, if it is not present there, the second most common finger (over 25%) are found on the middle finger.
This means that over 75% of these patterns, will be found on four of the ten possible fingers.
Much like the loop pattern, the friction ridge flow of the whorl pattern is often to the ulnar side (little finger side) of the hand. However, with whorls, it is the angle of the pattern which is commonly seen demonstrating this ulnar inclination.
As you see in the image here, when moving through the middle of the pattern, from top to bottom, it appears the angle is to the right. This is an indication, the finger that left this impression is more likely from the right hand.
And, if the radial inclination is observed, it is most likely from the left forefinger, as well.
Clockwise or Counter-Clockwise
The angle or slant of the pattern, is not the only aspect of a whorl which may provide insights. When the whorl is a spiral, or double loop, pattern. The rotation of the pattern can provide insights as well.
When moving from the inner core, to the outer area, does the pattern move in a clockwise or counter clockwise rotation?
If it is in a clockwise rotation, it is more likely for the impression to be from the left hand. Whereas, if counter-clockwise, it is more likely from the right.
Just as the flow of friction ridge impressions may help provide insights. When it comes to thumbs, there are unique aspects like the shape, size, and other features, as thumbs are not like other fingers.
In friction ridge impressions left by the thumb, there are several unique features, less commonly seen in other fingers, such as:
Shape of impression, larger, and at times pear shaped
Lower core, and larger number of visible ridges above
Found alone, not in a cluster
Tip ridges, with an ulnar inclination
No phalange seen beneath
Using Digit Determination
In the image below, by observing the impressions on the can. Can you provide some insights or observations that may support theories or conclusions that could be reasonably drawn from the evidence to answer questions like: which hand was holding the can?, how was it being held?, where may other impressions be on this exhibit?
This example is simplistic, but it helps demonstrate what else fingerprints may provide, before they establish identity.
If you like this example, check out the Fingerprint Museum, to practice your digit determination skills, or examine what contextual information you may draw from other impressions.
for Palm Impressions
Like fingerprints, palm impressions may also be found at crime scenes, like the image above. However, they are not always so clearly discernible as a palm impressions, and may be easily confused with fingerprints.
However, with a basic understanding of the features of palm impressions, you can use the visible location, orientation, and flow of the friction ridge detail to aid in not only determining if it is a palm impression, but also to narrow your search to specific area of the palm.
First, let's look at some of the terminology for the palm, and its features.
The palm can be divided to three main areas: Thenar, Hypothenar, and Interdigital. Each area has unique aspects, in friction ridge flow, that may provide aid in determining the area of the palm impression, as well as its overall orientation.
When considering anatomical factors for palm impressions, the two main aspects to consider is the flow of the friction ridges, and the major creases in the hand. On the human hand there are three main creases, formed before the friction ridge detail, which are very distinct:
Distal transverse crease - Runs from the outer edge of the hand to the area between the forefinger (index) and middle finger.
Proximal transverse crease - Runs from the thumb side edge of the hand, and ends in the middle of the hand. At the top, it may be joined to the Radial (thenar) crease.
Radial transverse crease - Runs from the thumb side edge down and around the Thenar side of the palm, towards the carpal delta, ending on the thenar side of the carpal delta.
One of the first features that clearly distinguishes palm impressions, is the presence of "crows feet"
This is a feature commonly found at the edge of creases on the palm, where the crease has clear bifurcations, and is common at the edge of the Distal crease.
Friction Ridge Flow
Another of the key features, which distinguish different areas of the palm impression, is the friction ridge flow. Below you can see:
How the flow is in a semi-circular flow from top to bottom, in the thenar area, and how much more pronounced the curve becomes as you move away from the thumb. With the longer side of the line being above the curved edge, versus below.
Whereas, in the hypothenar area, you see the ridges beginning to funnel together as they flow towards the centre of the hand. As well, in the opposite direction, the ridges flow to the side of the hand, in contrast to the thenar, where they flow to the bottom of the hand
Much like the thenar and hypothenar areas, flow of the friction ridges can help distinguish it from the others. In this area the ridges often flow somewhat parallel to the distal transverse crease, in a downward path to the ulnar (little finger) side of the hand. As well, this is the area of the hand, where we see the most deltas (triangular formation where three ridges create a triangular shape). In the interdigital area, there is commonly one beneath each finger, and the deltas commonly point to the middle area of the hand, with a flat edge beneath the finger.
In total, there are commonly no less than 5 deltas in the palm impression, with 4 being in the interdigital area. However, the other location where a delta is commonly found, is at the base of the palm, and this delta is referred to as a the carpal delta.
At the base is there the carpal delta is usually found alone, with no other deltas in the area. On one side the ridge flow will be from top to bottom (thenar side), on the other it will be top to side (hypothenar side) and at the base the flow is generally side to side.
Test Yourself ... What areas of the palm do you see?