most trace evidence is harder to analyze.
it must be sent to crime laboratories,where high-tech equipment can identify it.
For example, a laboratory may analyze broken window glass from a crime scene.
How does it bend light that shines into it ?
What chemicals is it made of?
With a report from the lab,a CSI can search a computer database for car models that have the right kind of glass.
Only a few models will match.
The police may not have found the exact crime car,but they will know what kinds to look for.