From Halopedia, the Halo wiki
During the Requiem Campaign, when Covenant and Promethean forces invaded the Infinity, Velasco was part of a group of Marines defending the engine room. While Fireteam Crimson was making their way there, Velasco radioed in that they were being overrun and couldn't hold the engine room much longer. Jared Miller told them to hold out for Spartan reinforcements. Velasco was cut off mid-sentence saying they were under heavy attack from Covenant forces.
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