From Halopedia, the Halo wiki
During the Requiem Campaign, he was assigned to "the Refuge." While he was there he studied Requiem's portal system along with Dr. Leslie Boyd. When Fireteam Crimson was at "the Gate," Ruiz directed them to a device that would stop the Prometheans from translocating into the area. After Crimson used the portal network, which the scientists had figured out how to control, to travel to "the Refuge," Prometheans attacked the Refuge base. During the attack, he identified the device that allowed the portals to open in the area, but wasn't able to shut it down. Crimson was able to destroy the device and turn off the portals in the area, halting the Promethean attack.
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