• Question: How do you extract a fingerprint from an object?

    Asked by kieran396 to Anna, Craig, Richard, Shane, Sue on 14 Jun 2011. This question was also asked by messedup.
    • Photo: Richard Case

      Richard Case answered on 13 Jun 2011:

      There are lots of ways to find and record fingerprints from objects.

      The most common way that you will see on tv shows is lightly brushing powders (usually aluminium) to a surface. The powder will stick to the sweat that is deposited when you put your fingers on an object. You can then either lift the powdered mark using a special kind of tape (or gel)… or photograph it. If it is a serious crime, then the CSI might use a laser to look for fingerprints.

      Sometimes a CSI will decide to send objects to a lab so that they can be subjected to chemicals that can bring out fingerprints. Common ones:

      Ninhydrin or DFO – both commonly used to find fingerprints on paper.
      Cyanoacrylate (often known as Super Glue) – can develop prints on metals and plastics

      A lot of research in this area is being carried out by the Home Office Centre for Applied Science and Technolgy (CAST) http://www.homeoffice.gov.uk/science-research/hosdb/… more info on their archived site http://tna.europarchive.org/20100413151426/http://scienceandresearch.homeoffice.gov.uk/hosdb/fingerprints-footwear-marks/index.html

    • Photo: Sue Carney

      Sue Carney answered on 13 Jun 2011:

      Seeing Richard’s answer here, there isn’t anything more for me to add. There are lots of methods of making fingerprints visible and of photographing them, but you need to be an expert like Richard, to know which ones to use when.

    • Photo: Shane Pennington-Cooper

      Shane Pennington-Cooper answered on 13 Jun 2011:

      This is pretty much a text book answer from Richard, there are a few things I would like to add:

      The method you use for fingerprinting is solely dependant on the material that the fingerprint is on. If the finger print was found on paper such as a questioned document you may want to use Iodine over Ninhydrin, the iodine crystals evaporate causing the vapours to adhere to the fats in the fingerprint, the advantage of this is it is not a destructive technique and would not interfere with any other material found such as skin fragments or small traces of hair. The trouble is the iodine method is only temporary so use of photograph is definitely recommended.

      Cyanoacrylate of known to some people as super glue fuming is the best method for larger areas such as inside cars as the vapours cover a wider area, word of warning though super glue fumes are highly toxic and should be used with standard safety precautions.

      I highly recommend you visit the sites Richard has kindly provided as this area of forensic science is fascinating, also research about Galtons details.

    • Photo: Anna Williams

      Anna Williams answered on 13 Jun 2011:

      What he said! 😉

    • Photo: Craig McKenzie

      Craig McKenzie answered on 14 Jun 2011:

      Hi Kieran,

      sorry it took me a little longer to get back to you on this one – Richard has given a very good answer and is an expert in this area (I am definitely not!) but I want to add a couple of other points to the answers you have been given.

      It is very important to extract or recover a fingerprint from an object but it is also important to know where to find a fingerprint in a crime scene in the first place and what it means when you do find it. One of the first things we do in a crime scene is look for contact points – this is where the suspect or whoever it is we are considering would have come into contact with objects in the scene – how did they come in and how did they leave? We have to put ourselves in their heads and look at their motives to think where are the most likely places they would have touched (if they weren’t wearing gloves).

      We also have to think if they had an innocent reason to have left a fingerprint behind before the crime occured – this might be whether or not they have been in the house / crime scene and could have left a fingerprint at that time and we call this ‘legitimate access’. This would have an important effect on how we would figure out the meaning of finding the fingerprint.

      If they were wearing gloves they probably wouldn’t leave fingerprints at the crime scene – but that doesn’t mean they won’t leave evidence behind – can you think of another type of evidence they might leave behind if they were wearing gloves that a forensic scientist might recover?

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