Antonio Quintero was an SD-6 agent.
Season 1[]
Quintero was gathering information about the Mueller Device in Taipei while working undercover inside an FTL cover station. Quintero sent information about the device to SD-6, but when it came time for him to report his intel in person, he didn't show up. Although no body was found, SD-6 assumed he had been captured or killed.
Three months after Danny Hecht was murdered, Dixon showed up at Sydney's campus and told her that Quintero was indeed killed by FTL agents.