POLICE now have a new test to help catch criminals and verify
alibis. By analysing the chemical composition of human hair,
researchers can determine the source of the water someone has
been drinking in recent months. And that can indicate where he
has been.  The technique depends upon studying isotopes. These
are naturally occurring variants of elements, which share the
same chemical properties but have different weights because
their nuclei contain different numbers of neutrons. James
Ehleringer and Thure Cerling, at the University of Utah in Salt
Lake City, and their colleagues collected human hair from
barbers' shops in 65 American towns. They report in the
Proceedings of the National Academy of Sciences that isotopes in
hair closely match the hydrogen- and oxygen-isotope ratios found
in the local water.  This research has obvious implications for
law enforcement and is being used by Salt Lake county sheriffs
to help identify a murdered woman. Isotope analysis of her hair
revealed that she spent the years