From Halopedia, the Halo wiki
During the Battle of Mombasa, Glick took the opportunity to return to the NMPD and take revenge on those that he considered to have wronged him, including Roberto Bustamante and Jim Odingo. Glick took Mike Branley and Sadie Endesha hostage in the lobby of the NMPD HQ. Glick admitted to them that he killed the officers, rationalizing his actions with the knowledge that they were "all screwed anyway". The ex-cop would, moments later, meet his demise at the hands of a SWAT team, who were responding to a warning from Jim.
The NMPD public service announcer Stephen later lied to the public about the shooting, and touted Glick, Roberto, and Jim, as heroes who were gunned down by Covenant snipers, who were in turn killed by civilians.
The dead officers at the NMPD HQ were probably killed by Glick.
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