How To Take Fingerprints
Believe it or not, people have been taking fingerprints for thousands of years.
In ancient Babylonia, some 4,000 years ago, law officers would take the fingerprints of arrested suspects, whilst as far back as AD 650 in China, fingerprints were used instead of signatures on contracts. The first conviction in England based on fingerprint evidence occurred in 1902, and fingerprinting technology has been used extensively ever since.
So far, no two people have been shown to have the same fingerprints, not even identical twins. As such, fingerprinting is considered a highly reliable form of evidence.
But how do you take a fingerprint?
There are several ways to take someone’s fingerprints, including electronically, but we’ll focus on the classic ink and paper method.
- Set up your fingerprint card. You’ll need somewhere to record your suspect’s fingerprints. The FBI have a downloadable fingerprint form you can print off and use. Secure your card to a flat surface for recording the fingerprints - you don’t want it to move around when you’re taking your evidence.
- Get your fingerprint pad. In order to make a mark, the finger in question will first need to be rolled in ink. Porelon pads are specifically designed for the purpose of fingerprinting - but if you’re not a professional forensic investigator, you can use any old ink pad.
- Wash the suspect’s hands. Clean hands are a must for accurate recording. Your suspect needs to wash their hands with soap and water and thoroughly dry them.
- Control your suspect. You, the fingerprint recorder, must be the one to control the suspect’s finger when taking their print. Hold their thumb or finger whilst trying to keep the wrist and forearm level with the hand as this will make recording easier. Tell the suspect to not try and help, as this would only make getting an accurate reading harder.
- Start with the right thumb and roll over the ink. Place the side of the thumb nearest the forefinger on the ink pad, making sure the edge of the nail is next to the ink. You need to get ink covering the thumb from the top of the thumbpad to ¼ inch below the first joint. Roll the thumb across the inkpad, all the way to the opposite nail.
- Roll their thumb over the fingerprint card. In the same manner, and in the same direction as you rolled their thumb over the ink, you need to roll their thumb over the fingerprint card. Use light pressure, and roll at a steady pace, as pausing or applying differences in pressure can cause smudging. Roll only once and lift the thumb straight off afterwards, do not roll the thumb back and forth.
- Repeat with remaining fingers. Complete the same process of inking and recording for the remaining fingers on both hands.
Normally, fingerprints are digitally analysed to search for matches with other prints that are on record. Prior to the invention of computers, this was a tediously manual task.
Analysts look for 3 key types of pattern when comparing fingerprints.
- Loops - these are patterns which curve back on themselves to form a loop shape, they make up roughly 60% of pattern types.
- Whorls - are spiral or circular patterns, often contained within each other, which make up approximately 35% of pattern types.
- Arches appear as a wave-like form in the fingerprint, and account for 5% of patterns.
Have a look at your suspect’s fingerprints to see if you can spot the different types of pattern.
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