What is “Match Analysis”?

Broken plastic from a vehicle accident

When items are “broken” they form unique edges. The manner in which an item breaks is random because the force and direction of force applied is random.  Because these edges are formed randomly they may be considered individual characteristics (depending on how well defined the edges are).  Whether it’s a traffic accident, assault, vandalism, or homicide if certain broken pieces are left behind by the suspect at the crime scene then the potential exists to link that suspect to the crime by their possession of the matching broken pieces. You’ve all probably read stories about hit and run accidents wherein parts of the suspect vehicle were left behind at the accident scene. If you’re really lucky you’ll find a bumper with the license plate still attached but usually it’s broken pieces of light housings or paint fragments. The same type of analysis can be done in any crime where items are broken. The critical aspect is that the broken pieces retain defined edges that can be compared to one another.

I have a simple experiment for you to try. Take a photograph or written document and make 5-10 photocopies of it.  Working with only one sheet of paper at a time then do the following.  Tear the page in half. Put the two halves together (doesn’t need to be aligned) and tear them in half again making four pieces. On the back of each piece write the numeral ”1″. Repeat the process, one page at a time, labeling each group sequentially (second page is group “2″, third sheet is group “3″, etc.).  Take the four pages from group 1 and put them back together so the tears align. See how the edges of the tears fit together. Look closely at the images or words on the document and exactly where they are torn apart. Then assemble each group on the floor or a table so all of the assembled groups are in front of you (you’ll be looking at 5-10 identical documents).

Broken plastic pieces fit back together

Now comes the interesting part.  Take a piece from group 1 and see if you can make it fit into the corresponding area of any of the other documents. Then try another section. Can any of the torn pieces be “fit” convincingly into any of the other identical documents? The answer is no.  Congratulations, you’ve just performed your first “match analysis”.  In your story line you may have a scene where a suspect beats a victim with a pool cue that breaks in half. He leaves the tip at the scene and dumps the other end in his car. Or maybe you have two people fighting over a document which tears in half.

Actually, when I used to collect carpet samples of bloodstains I would cut them out in different geometric shapes and photograph the spots they were taken from afterwards. That way, if there became a question later in court about the location it was collected from, that particular shaped sample could only “fit” back into one (and in one orientation) location in the crime scene.  Same principle, just a different purpose.