In Justice League: Cry for Justice #2 (2009), while volunteering as night guards at Flash Museum, they were killed by an unknown assailant who steals the Cosmic Treadmill.
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In a possible future where members of the current incarnation of the Teen Titans mature into a corrupt and tyrannical Justice League, the Cosmic Treadmill is absent from the Flash Museum; it is instead kept in a more secure location inside the Batcave, presumably to ensure that their "enemies"—in truth, a group of right-minded Titans—cannot alter the past and change their timeline.