Three seemingly unrelated deaths proved to be serial murders; the killer had been careful, he used poison which had no taste or odour; fortunately for investigators, it also has a unique chemical signature.
The owner of a restaurant is killed; investigators uncover tales of debt and deceit, but the case remains open, until one detective gets inspired by an earlier episode of "Forensic Files," and looks for clues in an empty holster.
A serial arsonist was on the loose in Washington, DC. Each of the fires was started with the same type of incendiary device. The perpetrator was very careful, and seemed to leave no evidence behind... but there were clues in the ashes, and it was up to forensic scientists to find them.
A killer tried to destroy everything which could link them to the crime; but in doing so, they inadvertently created new forensic evidence, evidence which came to light using a technique never before used in a criminal investigation.