Abra Cadaver - S3-E5
Corrected entry: When Catherine and Nick are investigating the rock star's death and find the needle in his arm, why wouldn't they have just checked for prints on the syringe? In the flashback later on, it is shown that the murderer did not use gloves, and therefore her prints should be on the syringe.
Correction: The scene and show did not remotely indicate whether or not the villain wiped their fingerprints or not, which most guilty people do. Nor did the sequence indicate at all how much time the crime scene took place over as oppsed to time spent on screen. These two concepts together imply a legitimate counter to your mistake/.