DISTURBING CONTENT WARNING:

A Georgia man accused of fatally stabbing a 66-year-old great-grandmother in an unprovoked attack aboard an Atlanta MARTA train is now facing a federal charge that could make him eligible for life in prison or the death penalty, federal prosecutors said.

John Elijah Matthews, 25, of Decatur, Georgia, was charged in a federal criminal complaint with committing an act of violence using a dangerous weapon with intent to cause death on a mass transportation system, according to the U.S. Attorney’s Office for the Northern District of Georgia.

Acting Attorney General Todd Blanche will determine whether the government will seek the death penalty if Matthews is convicted, prosecutors said.

The victim, identified by federal officials as Margaret Swan, 66, was described by U.S. Attorney Theodore Hertzberg as a “beloved great-grandmother” who was killed in “an unprovoked act of senseless violence.”

DISTURBING CONTENT WARNING: ILLEGAL ACCUSED OF KILLING GEORGIA GRANDMOTHER FACES NEW DISTURBING CHARGES

The deadly attack unfolded around 11:25 a.m. Saturday, May 30, while Swan was riding a northbound MARTA train from the Lakewood station toward Oakland City Station, according to prosecutors and a Fulton County arrest warrant affidavit obtained by Fox News Digital.

The affidavit, sworn by MARTA Police Detective Douglas Burn, alleges Matthews boarded Train Car 134 at 11:24:59 a.m., wearing glasses, an orange T-shirt with writing on the front, dark gray pants, white socks and black slides. Swan had boarded the same train car minutes earlier, at 11:21:46 a.m., and was sitting alone, according to the affidavit.

Surveillance video allegedly showed Matthews walk to the side of the train where Swan was seated and stand near her.

At 11:25:18 a.m., he allegedly moved closer and stood just to her right. Eight seconds later, at 11:25:26 a.m., he allegedly reached into his right front pants pocket, pulled out a knife and opened it, the affidavit states.

At 11:25:32 a.m., Matthews allegedly sliced Swan’s throat with his right hand while holding her head, according to the affidavit. Swan screamed and tried to get up from her seat, but Matthews allegedly held onto her right arm and stabbed her approximately 18 to 20 times, the affidavit says.

Federal prosecutors said surveillance video showed Matthews stabbing Swan approximately 18 to 20 times in the chest and neck area as she tried to defend herself.

Other passengers fled and called for help, and at least one passenger confirmed Swan had no interaction with Matthews before the attack, prosecutors said.

ILLEGAL IMMIGRANT RELEASED BY BIDEN ADMIN PLEADS NOT GUILTY TO MURDER OF GEORGIA GRANDMOTHER

The affidavit says Matthews then threw Swan to the floor and stood near her until the train arrived at Oakland City Station at 11:27:05 a.m.

He then allegedly exited the train with the knife in his right hand and walked toward the north end of the platform.

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MARTA police officers arrived moments later and rushed to apprehend him, according to the affidavit.

Officer Bolton, who was patrolling the Oakland City Station concourse, heard a commotion on the platform and saw patrons pointing toward Matthews, according to the affidavit.

Bolton allegedly saw Matthews holding a knife near the north end of the platform and ordered him to turn over. Matthews allegedly did not comply and was taken into custody after another officer arrived, the affidavit says.

CHARLOTTE RESIDENTS SAY THEY FEEL LESS SAFE AS CITY FACES SECOND TRANSIT STABBING

Prosecutors said Matthews was allegedly found with a bloody folding knife and had blood on his clothes. The affidavit says that Matthews “did not have an address currently” and that he advised he did not have a phone number currently.

First responders attempted emergency medical aid, but Swan was pronounced dead at the scene.

The affidavit says the Fulton County Medical Examiner arrived at the scene at 1:45 p.m. and recorded Swan’s time of death as 2 p.m.

WATCH: Atlanta train riders on edge after deadly stabbing

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Matthews remains in local custody and will appear in federal court. The case is being investigated by the FBI and the Metropolitan Atlanta Rapid Transit Authority Police Department.

“This crime also impacts everyone who relies on mass transportation to move about their daily lives. Using Atlanta’s train system should be safe and free of violence,” said Marlo Graham, special agent in charge of FBI Atlanta.

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He is also charged locally with felony murder, according to Fulton County records. Fox News Digital has reached out to MARTA, the Fulton County Sheriff’s Office and the U.S. Attorney’s Office, Northern District of Georgia for additional information.