JACKSONVILLE BEACH, Fla. -- A 13-year-old girl died Wednesday afternoon, about 18 hours after a man shot into a van full of children, fled from police and took two hostages during an eight-hour standoff.

Brianna Maria Ganas, of Jacksonville, died at Shands-Jacksonville Medical Center. Ganas' aunt, Aja Leigh McKenna, 26, of Jacksonville Beach, was also shot. Her condition was upgraded to serious.

Flying glass injured two younger children in the van.

The gunman, Paul Christian Rentas-Rivera, 29, of Orlando, Fla., surrendered early Wednesday after a SWAT unit fired canisters of tear gas into the apartment.

He is charged with one count of first-degree murder, one count of attempted murder, one count of kidnapping and one count of burglary. He is being held without bond in the Duval County jail.

Police said Rentas-Rivera began shooting when McKenna, his girlfriend, started to drive away after an argument. Witnesses told police the assailant fired 15 shots at the minivan.

Family members said Ganas was trying to cover her aunt's body with her own when she was fatally shot.

"When her auntie got shot, Brianna went to try to help cover her," said Sunshine Kight, who raised Ganas. "It sounded like her."

Kight called Ganas a beautiful and cheerful girl who "would do anything to help somebody else." The 13-year-old did just that, and it cost Ganas her life.

The family made the difficult decision of taking Ganas off life support Wednesday.

"I think everybody's doing just a little bit of their own (grieving), just trying to get through it," Kight said.

McKenna fled to the Third Street Diner, where employees called police just before 7 p.m. Tuesday.

Three other children in the van, an 8-year-old boy and two girls ages 4 and 11, were treated at a hospital for minor injuries and released, officials said.

Police pursued Rentas-Rivera on foot to an apartment building about five blocks away, where he broke into a second-floor apartment. Two people inside the apartment were briefly held at gunpoint, then released unharmed, Jacksonville Beach police spokesman Michael Zdunkiewicz said.

Zdunkiewicz said police officials negotiated with Rentas-Rivera before tear gas was fired into the apartment at about 3:45 a.m.

Rentas-Rivera made no demands during the standoff, except to ask for cigarettes, Zdunkiewicz said.

Channel 4 learned that Rentas-Rivera was arrested in March on charges he had beaten, handcuffed and stabbed McKenna. She told police at that time that he threatened to kill her and her children if she left him.