Sergeant accused of sending explicit messages to undercover officer posing as teen: Court docsHARRIS COUNTY, Texas (KTRK) -- A sergeant with the Harris County Sheriff's Department is now in federal custody, just days after being arrested on state charges. He is now facing similar charges in federal court following his initial arrest. Federal documents detail explicit online messages Black allegedly exchanged with an undercover officer who was posing as a 13-year-old girl. Authorities allege he initiated direct messages with the undercover officer and continued communicating after being told the individual was underage. undercover officer said.