# How was this forensic science result determined? **URL:** \ **Category:** Factual Questions\ **Created:** [June 9, 2011, 4:49pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871 "2011-06-09T16:49:23Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![rogerbox](https://avatars.discourse-cdn.com/v4/letter/r/76d3ee/32.png) [@rogerbox](https://boards.straightdope.com/u/rogerbox)\ **Post date:** [June 9, 2011, 4:49pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/1 "2011-06-09T16:49:23Z")
I was reading at [this](http://www.trutv.com/library/crime/serial_killers/unsolved/hair_in_hand_murders/5.html) site the following: > [@](#): > > According to Dr. Black, he and his team were able to determine that the strands of hair represented nine months’ growth and belonged to a person who lived in the United Kingdom. The person, however, had traveled abroad on two occasions, and had changed their diet twice in the three months prior to the hair being cut. According to a Dorset Police document, the person in question had traveled to “the Valencia-to-Almeria area of eastern Spain and/or the Marseille-to-Perpignan area of southern France for up to six days,” approximately eleven weeks before the strands were cut. Afterward, the person visited an urban area of Tampa, Florida., for eight days, approximately two to two and a half weeks before the hair was cut. I can easily believe that the hair strands like a ring of a tree, can show diet changes over time. But how can they single out with such astonishing accuracy where the person had been? I would be impressed with “Went from a clean rural place to a polluted urban inner city”, but police in the UK can tell when someone had been to TAMPA by their hair? :dubious: ---
**Author:** ![ethelbert](https://avatars.discourse-cdn.com/v4/letter/e/958977/32.png) [@ethelbert](https://boards.straightdope.com/u/ethelbert)\ **Post date:** [June 9, 2011, 5:13pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/2 "2011-06-09T17:13:41Z")
This is just a WAG, but I seem to recall that differences in drinking water can sometimes be used to pinpoint a person’s whereabouts from their hair (e;g some areas have a specific mineral signature). ---
**Author:** ![rogerbox](https://avatars.discourse-cdn.com/v4/letter/r/76d3ee/32.png) [@rogerbox](https://boards.straightdope.com/u/rogerbox)\ **Post date:** [June 9, 2011, 5:21pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/3 "2011-06-09T17:21:52Z")
That sounds plausible, but is there some database of worldwide drinking water mineral signatures that forensic investigators have access to? ---
**Author:** ![robert\_columbia](https://avatars.discourse-cdn.com/v4/letter/r/e79b87/32.png) [@robert\_columbia](https://boards.straightdope.com/u/robert_columbia)\ **Post date:** [June 9, 2011, 7:00pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/4 "2011-06-09T19:00:44Z")
> **[Science Montage](https://xkcd.com/683/)** > > The rat's perturbed; it must sense nanobots! Code grey! We have a Helvetica scenario! ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [June 9, 2011, 11:10pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/5 "2011-06-09T23:10:53Z")
This was _Isotope Analysis_. Geologists have pretty good databases of isotope distribution, as it can be used for a range of analysis. Forensic Scientists just tap in to that data. Si ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 10, 2011, 2:43am UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/6 "2011-06-10T02:43:02Z")
What isotopes would they use? Organic material like hair is mostly made up of lightweight elements like carbon, hydrogen, oxygen, and nitrogen, and most of those only have one stable isotope. Do they use the trace amounts of heavier elements, or is there something useful they can get out of the common ones? ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [June 10, 2011, 10:56am UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/7 "2011-06-10T10:56:55Z")
Strontium and Oxygen, according to [wiki](http://en.wikipedia.org/wiki/Isotope_analysis#Forensics). Si ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 10, 2011, 4:53pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/8 "2011-06-10T16:53:10Z")
So a little of each, then. Hm, I hadn’t realized that there were other stable isotopes of oxygen. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [June 10, 2011, 7:29pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/9 "2011-06-10T19:29:42Z")
[sup]16[/sup]O/[sup]18[/sup]O ratios are used to study historical climate effects from ice cores, because there is a temperature dependent variation. Si ---
**Author:** ![Markxxx](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@Markxxx](https://boards.straightdope.com/u/Markxxx)\ **Post date:** [June 10, 2011, 11:00pm UTC](https://boards.straightdope.com/t/how-was-this-forensic-science-result-determined/584871/10 "2011-06-10T23:00:48Z")
They do it like with all DNA. The figure out what probably happened, then get a hair and confront the person with what they think happened. > [@](#): > > Police ) We got you > Guilty) You do not > Police) We have a hair with your DNA, which is always 100% correct > Guilty) OK I’m guilty 🙂