- "We were good, Colonel. Every bit as good as you. We believed what we were doing was for the good of the country. And if you hadn't put me in here, we might have had our own Sentinel by now."
- ―Sean Grieves[src]
He would help steal alien technology to be sent back to Earth to help the fight against the Goa'uld. On one of his missions, the leader of the Latonans, called Marul, had denied the team's request to see the Sentinel, a powerful device capable of sending away any Goa'uld threat. Grieves and Lt. Kershaw went behind the locals' backs and worked under the cover of darkness, dismantling the device, studying it and returning it exactly the way they found it, except they killed the Caretaker in the process. Colonel Jack O'Neill captured him and the rest of his team using an Asgard mothership to pin them down. He returned to Earth and was immediately arrested and charged with treason against the United States and its allies. (SG1: "Shades of Grey", "The Sentinel")
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Grieves was on death row when O'Neill offered him a pardon from the sentence to return to the planet Latona and fix a problem he and his associate, Kershaw, had started. He eventually sacrificed himself to repair the Sentinel. (SG1: "The Sentinel")