Greg Sanders became a field investigator during Season 5 of CSI: Crime Scene Investigation.
Greg began the series as a gifted laboratory technician and DNA analyst working behind the scenes at the Las Vegas Crime Lab. Although he was enthusiastic, knowledgeable, and sometimes eccentric, he wanted to become a full-fledged crime scene investigator and work cases alongside Grissom, Catherine, Sara, Nick, and Warrick.
His transition unfolded during the fifth season. In the season premiere, "Viva Las Vegas," Greg worked his first field case while Chandra Moore replaced him in the DNA lab. He then continued developing his practical skills and completed the required proficiency process, ultimately moving from laboratory work into regular crime-scene investigations.
The change was more than a job promotion: it reshaped Greg's role in the series. He gained substantially more contact with victims, suspects, and evidence at active scenes, while the show explored the difference between laboratory expertise and field judgment. Viewers sometimes associate the transition with "Who Shot Sherlock?" because Greg's proficiency test is central to that episode, but the broader move belongs to Season 5.