From Halopedia, the Halo wiki
Muir was present on New Llanelli when the Covenant attacked and glassed the colony in 2546. He survived the attack, and managed to survive alone on New Llanelli for nearly seven years.
In early 2553, ships belonging to Captain Serin Osman and Avu Med 'Telcam landed on the planet. Muir saw the ships, as well as trailers carrying smuggled weaponry being driven away, but not the actual meetings or the trailer's contents.
Staff Sergeant Malcolm Geffen spotted him after the second meeting and eventually captured him. Osman decided to have him quarantined on the ship, so he couldn't discover anything else about her mission. When he questioned Osman about the meetings, she lied and told him they were exchanging fallen soldiers. Muir believed the lie, sparing Osman from having to eliminate him as a security risk. He was later transferred to the UNSC Monte Cassino prior to the ship's return to Earth.
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