From Halopedia, the Halo wiki
The Donoma had dropped out of Slipstream Space into the Deep Space Transitional Zone outside of the Tisiphone System. There, it was boarded by Jiralhanae forces. In the assault, the bridge was attacked and the ship decompressed twice. Many of the bodies of the crew blew out into space.
Incident Response and Investigation teams were sent in to the remains and tagged many elements around the ship. On December 8, 2553, Rear Admiral Serin Osman, Veta Lopis and her Ferret team investigated the remains of the ship. Rear Admiral Osman suspected The Banished to be the culprit, but Veta Lopis ruled this out. This investigation was the start of Operation: RETRIBUTION.
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