A Mexican national in the United States illegally when he allegedly shot and killed a Baton Rouge boy on the teen's 16th birthday in March was sentenced to two years in federal prison Thursday on gun and immigration charges stemming from the fatal shooting.

Octavio Bringas-Posadas, 50, also is under indictment in state court on a negligent homicide charge in the killing of Darius Plummer at Bringas-Posadas' Southpark Drive apartment off Airline Highway. Plummer was the best friend of Bringas-Posadas' son.

Assistant Federal Public Defender Mark Upton told U.S. District Judge Shelly Dick that Bringas-Posadas, who pleaded guilty in June to the federal charges, also intends to accept responsibility for Plummer's death in state court.

Bringas-Posadas asked Dick for forgiveness through an interpreter and said he is very remorseful.

"He says he is remorseful? He wasn't remorseful when he fled," Plummer's mother, Trina Plummer, said outside Dick's courtroom after Bringas-Posadas was sentenced.

Police have said Bringas-Posadas told a relative he was playing with a gun on March 13 when it fired by accident and struck the boy. He also told the relative on the phone that he was not coming back to Baton Rouge and would not talk with police, according to his arrest warrant. Bringas-Posadas was stopped on Interstate 10 in Lake Charles.

"It's just pure ignorance, carelessness," Trina Plummer said of Bringas-Posadas' actions. She said Bringas-Posadas' son also was present at the shooting and could have been hit.

Upton called the fatal shooting a "massive tragedy."

"He is incredibly remorseful," Upton told Dick. "If he could he would take it back and change places."

Negligent homicide carries up to five years in prison. Bringas-Posadas pleaded not guilty to that charge in August. His next appearance in state court is Nov. 20.

"He is ready to go forth and accept responsibility (in state court) as he has in this court," Upton told the judge.

Dick said Bringas-Posadas' two-year term will run concurrent with whatever sentence he might receive in state court in the fatal shooting.

Bringas-Posadas was deported to Mexico in 2012 after a Baton Rouge drug arrest but later returned to the United States.

Dick has said he is likely to be deported again.

The judge also ordered Bringas-Posadas to forfeit three handguns and ammunition found during a search of his car and apartment.

Follow Joe Gyan Jr. on Twitter, @JoeGyanJr.