Marcus Geier is a forensic technician with the FBI. His first broadcast appearance was as an unnamed tech in the second-season episode "Spaceman in a Crater". (He had previously been in "Player Under Pressure", an episode which was not aired until the following year.) In the third season, the character was given a name and used in several episodes, starting with "Soccer Mom in the Mini-Van". His role is to present evidence discovered at a crime scene to Booth and/or the squints.