Federal investigators are taking on the case of the the Union City teen shot and killed by police last December.

"The U.S. Attorney's Office and the FBI will look in to the shooting death of Ariston Waiters to determine whether any federal laws were violated," Executive Assistant U.S. Attorney Charysse Alexander told The Atlanta Journal-Constitution on Wednesday.

The decision was made following an impromptu meeting between U.S. Attorney Sally Quillian Yates and state Sen. Vincent D. Fort (D-Atlanta) late Wednesday morning.

Fort was accompanied by Waiters' mother, Freda Waiters, her attorney Mawuli Mel Davis, several family members and community activists as they gathered to deliver a letter to Yates requesting her aid in the case.

"It was an illegal arrest," Fort told the AJC following the meeting. "Even [Fulton County District Attorney] Paul Howard said Ariston never should've been arrested."

Ariston Waiters, 19, was shot and killed after an altercation with Union City Police Officer Luther Lewis on the night of Dec. 14. Last week, a Fulton County grand jury decided not to indict Lewis for any criminal action in Waiters' death.

Union City police officials have maintained that Lewis was justified in his actions, saying in a statement released in January that Waiters “grabbed the officer’s service weapon” as he was being handcuffed. He was being taken into custody in connection with a report of shots being fired.

"When the grand jury failed to indict, we thought that was the wrong decision," Fort said.

The opportunity to speak with Yates came as a surprise.

"She very graciously set aside some time to meet with Sen. Fort and Ms. Waiters," Davis said.

Alexander said that the federal investigation would begin "immediately."

Fort said he would gladly wait to meet with Yates to hear the outcome of the federal investigation.

"While we understand that the U.S. Attorney can't give us a time frame, we still have a sense of urgency about this," he said.