NOVA Online: Bombing of America


image of hair on television monitor

If hair is found at a bomb explosion site, it may be of some help in determining who set the bomb. When a strand of hair is studied under a microscope, it definitively reveals:
  • the ethnic background of the individual
  • where on the body the hair came from
It might also reveal:
  • overall color
  • whether the hair was chemically treated
  • whether the hair was forcibly removed or shed
  • length
  • thickness
  • how the hair was cut*
*This only works if hair from a suspect's head is compared with hair found at the bomb site very soon after the explosion.

Where the hair was found makes a difference to the investigator. Hair found in debris is relatively useless, since it is hard to prove that it "belongs" to the bomb site. Hair found on a piece of tape near the explosion is much more valuable.

It may seem surprising that hair is found at all after an explosion. Keep in mind that, on average, humans shed about 100 hairs a day. A criminal may shed hair while taping a bomb together, and that hair can get stuck to a piece of tape. When the bomb explodes, the tape around it flies off very quickly, sometimes ahead of the flames.

The Procedure

After a series of tests are performed on the bomb site hair sample, the investigator might ask to see hair from the suspect's head. The "known" hair sample is subjected to all the same tests as the bomb site sample, and then the known hair and bomb site hair are studied side by side under a comparative microscope.

The kind of information an investigator can glean from these tests is helpful, but, afterward, the investigator is only able to say that a piece of hair might have come from a particular person.

More definitive hair tests

When a strand of hair is found intact - with the root, or bulb, in place - it can be subjected to regular DNA testing. The reason the root or bulb needs to be intact is that the amount of DNA in a shaft, or strand, of hair is insufficient for analysis. Hair with the root intact will have cells attached to it that are from the living tissue of the scalp. This living tissue will contain enough DNA for a specialist to analyze.

Recently, another kind of DNA testing has been used to analyze hair: Mitochondrial DNA testing.

Examining other physical evidence:

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