Analyzing Crime Scene Clues

Imagine the heartbreak of having your young child mysteriously disappear from a holiday party…as happened to a northern Virginia family some years ago.

Now imagine you’re the FBI agent trying desperately to solve the case, but with no sign of the missing 5-year-old and little evidence to go on. Your prime suspect is the maintenance man at the apartment complex where the child lived. In his car you find tiny bits of hair and clothing fibers. Will this evidence be your link to the missing child, the break you need to solve the investigation?

In this case…as in many cases like it before and since…the answer was yes—thanks to the work of forensic experts in our FBI Laboratory. After careful analysis, our scientists found that the hairs were highly similar to the missing girl’s and that the fibers were no different from those on a rabbit hair coat worn by the child’s mother. Even though the 5-year-old was never found, this trace evidence—as we call it because it’s small and easily transferred—played a key role in putting the killer behind bars.

Each year, some 10,000 bits of this kind of evidence—shards of glass, strands of hair and fur, paint chips, soil clods, feathers, rocks and minerals, building materials of all kinds, you name it—come pouring into what we call our Trace Evidence Unit on the third floor of our FBI Lab in rural Virginia, courtesy of not just FBI investigators but also any law enforcement agency nationwide looking for help in a case.

There, it is compared, contrasted, and analyzed every which way for whatever clues may lie hidden, usually invisible to the naked eye. A lot can be learned in the process.

Just a few examples: We can tell if a strand of hair is dyed or burned; whether it’s from an animal or human being; what part of the body it’s from; and whether it was shed or pulled out. When glass is fractured, we can determine the direction of the blow and what did the damage. We can take the smallest pieces of building materials and figure out if they are insulation, fiber glass, building tile, bricks, cement blocks, etc.

“It’s amazing how the smallest clues can end up yielding so much information and making such a big difference in cases,” says Cary Oien, chief of the unit.

Here are some more details about the work of the unit:

The people. Highly professional and well-schooled. Along with Oien, the 18-person staff includes: forensic examiners who do the evidence comparisons, write reports, and testify in court … physical scientists who prepare and process the evidence … and a geologist who specializes in mineralogy and soil comparisons.

Tools and techniques. For soil, a technique called “x-ray diffraction” is used. For glass, it’s the glass refractive index measurement (yes, “GRIM” for short). For fiber, we use tools like the microspectrophotometer and infrared spectrophotometer to discriminate between colors and types of polymers (polyester vs. wool, for example). And of course, there are plenty of powerful microscopes on hand.

Cases. More than we can name. But including: 9/11, the D.C. snipers, the ’01 anthrax attacks, O.J. Simpson, and plenty of violent crimes and kidnappings.

Final words. “We’re all about using science to solve crimes,” says Oien. “But there is a very personal side to what we do. Some of the cases we’re involved in—whether it’s a missing child or a brutal murder—are heart wrenching. It’s a great feeling when our analysis helps take a dangerous criminal off the streets. That’s what makes every day here interesting and worthwhile.”

Thanks to the FBI