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A man and a woman were sentenced Monday to 13 and six years in prison, respectively, for joining a group of Confederate flag supporters who in 2015 drove around a small Georgia community threatening people, including a gathering of African-Americans celebrating a young boy's birthday.

The attack, prosecuted under the state's Street Gang Terrorism law, came several weeks after a white supremacist killed nine black worshipers at a South Carolina church, sparking a backlash against public displays of the Confederate battle flag.

Related: Rebel Flag Fans Face Gang Charge for Crashing Black Kid’s Party

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Jose Ismael Torres and Kayla Rae Norton Douglas County Sheriff's Office

The Georgia group called itself Respect the Flag, and prior to the attack was seen driving in a convoy of trucks flying rebel flags, shouting threats at black people, authorities said.

The two sentenced Monday, Jose Torres and Kayla Norton, who authorities said yelled racist slurs and threatened the birthday revelers with a shotgun, were the last of the group to be sentenced. They wept in a Douglas County courtroom as a judge imposed their punishments: Torres, 26, convicted of aggravated assault, making terroristic threats and a violating street-gang statute, received 13 years in prison and another seven on probation; Norton, 25, convicted of making terroristic threats and violating the gang law, will serve 6 years in prison and nine on probation.

Both were also banished from Douglas County, a racially diverse community a few miles west of Atlanta.

Douglas County District Attorney Brian Fortner said in an interview that the prosecution of the attack began with people with less serious involvement, and moved in toward those who drove it.

Two other people have received prison sentences, while the rest of those involved, about a dozen, did not get prison time but pleaded guilty to misdemeanors or entered pre-trial diversion programs, Fortner said.

Local police came under fire on the day of the attack for choosing not to arrest any of the aggressors. But the Douglasville Police Department eventually built the case for prosecution, Fortner said.

The investigation included a review of thousands of Facebook pages that identified members of the Respect the Flag as white supremacists who discussed attending Ku Klux Klan rallies, joining a skinhead group and made derogatory remarks about black people, Fortner said.