JACKSONVILLE, Fla. – A 16-year-old boy has been charged in a triple shooting that left a 19-year-old dead Friday after a high school football game in Northwest Jacksonville, Jacksonville Sheriff Mike Williams announced Tuesday.

Robert Howard was arrested Tuesday morning after he was identified by witnesses as the shooter, Williams said.

Howard, a student at Grand Park Alternative School, is charged with second-degree murder and two counts of attempted murder in the shooting at Raines High School.

He will make his first appearance in juvenile court Wednesday. Howard will eventually be charged as an adult.

WATCH: Jacksonville sheriff announces teenager's arrest in deadly triple shooting

IMAGES: Scene after triple shooting outside Raines' football stadium

The triple shooting happened about 10 p.m., about 15 minutes after the game between the Vikings and the Lee High School Generals ended at the school off Moncrief Road West in Northwest Jacksonville.

Joerod Adams, 19, was killed, and a 16-year-old girl who attends Lee High and a 17-year-old boy who attends Raines High were wounded.

The girl, who was hit by a stray bullet in her lower body, was treated and released, and the boy, who was wounded in his upper body, was in stable condition in a hospital Tuesday, Williams said.

Police said Adams and the other boy were direct targets in the shooting, and the teenage girl appeared to have been collateral damage.

“Where does a 16-year-old think it’s OK to murder someone in cold blood at a football game?” Williams asked during a news conference announcing Howard's arrest.

Williams said Adams had been ejected from the stands Friday night by the Duval County School Board police after he got into a fight. Williams said Adams and the injured 17-year-old, who were at the game together, got into a confrontation with Howard inside the stadium during the second half.

He said Howard targeted them with a handgun when they met later on a sidewalk outside.

Homicide detectives said all three boys have known ties to criminal gangs, and it's unclear if the motive for the shooting was related to gang activity or the fight inside the stadium.

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School District Police Director Micheal Edwards said the shots were fired close to where officers had checked everyone entering the gates into the stadium with a metal detector. He said because there were more than 50 police officers at the game, there was an immediate response.

State Attorney Melissa Nelson said despite the arrest, police and prosecutors still need help in the case and anyone who saw the shooting or the events leading up to it or who knows someone who did should call police at 904-630-0500.

She said that Howard was arrested in April for carrying a concealed weapon but that the charge was dropped because of evidentiary issues.

Since the shooting, security was beefed up at both Raines and Lee high schools, along with Ribault High School. Duval County Public Schools also announced about a dozen high school football games expected to draw big crowds will be moved to either Saturday mornings or 5:30 p.m. Thursdays.

19-year-old victim's family fearful despite arrest

While Adams' family members said they were pleased an arrest was made, they said they did not want to make any public comments because they had received threats.

Adams' relatives told News4Jax that they and the mother of the 17-year-old boy who was wounded in the shooting have been receiving telephone threats.

It’s unclear who’s making the threats. Adam's grandfather said police have been notified and a detective stopped by his home Tuesday.

Adams' family members said they believe three others were with Howard Friday night.

The Sheriff's Office has not confirmed other suspects. The case is still under investigation.

No one answered the door when News4Jax went to the home listed as Howard's address on his police report.