A 19-year-old from Wilmington was charged in federal court Thursday with participating in Wednesday’s gunpoint carjacking of U.S. Rep. Mary Gay Scanlon in FDR Park.

Josiah Brown pleaded not guilty during a virtual arraignment to charges including carjacking and firearms violations. He will be held in custody as his case moves forward.

Federal authorities said Brown, along with a still-unidentified coconspirator, pointed a gun at Scanlon’s chest in the park around 2:30 p.m. and demanded her car keys. Scanlon handed over her belongings and was not physically harmed, they said, while Brown and his accomplice drove off in her 2017 Acura MDX.

Unbeknownst to the robbers, the SUV had a tracking device in it, according to charging documents filed in the case, and that allowed police to locate the vehicle within a few hours — first outside Brown’s house in Wilmington, and then at the Christiana Fashion Center in Newark, Del.

It was there that Brown was taken into custody along with four other teens around 8:30 p.m., police said. State troopers and federal agents initially saw Scanlon’s SUV unoccupied, but officers watched it and eventually saw the teens getting in. The teens tried to flee as police approached the car, officials said, but all were eventually arrested.

Only Brown was facing charges connected to the carjacking.

» READ MORE: Multiple people in custody after U.S. Rep Mary Gay Scanlon is carjacked and robbed in South Philly

The new details painted a fuller picture of an incident that quickly attracted national attention. Philadelphia police on Thursday held a news conference detailing the dangers of carjackings, which they said have been on the rise in the city over the last several years.

And U.S. Attorney Jennifer Arbittier Williams — whose office is prosecuting Brown — said the crime had national security implications due to Scanlon’s standing as an elected official.

“If you pick up a gun and use it to commit a crime, together we will come after you,” Williams said at an afternoon briefing. “And we are very good at what we do.”

Scanlon said during a virtual news conference that the episode was frightening, particularly because the gunmen appeared so young when they got out of their SUV.

“I was scared that someone would do something even more stupid than trying to steal a car,” Scanlon said.

Still, she was grateful that no one — including other residents or families using the park — was injured. And she said President Joe Biden was among the many who had since called to wish her well. She and Biden also discussed “common sense gun safety measures,” she said, such as enhanced background checks and potential regulations for ghost guns.

Scanlon was carjacked Wednesday afternoon, shortly after she and other elected officials met to discuss constituent concerns about development plans for the park. As Scanlon walked back to her car on the 1900 block of Pattison Avenue between 2:30 and 2:45, charging documents say, a black SUV pulled up in front of her and someone she was with.

Brown and another man got out and pointed a gun at Scanlon’s chest, the documents say. She handed over her keys and other belongings, and Brown and his accomplice drove away in her car while another coconspirator followed in the group’s original SUV.

Authorities have not provided further details about the people they think may have committed the carjacking with Brown, or said if they have a lead on the other suspects.

After he was arrested in Delaware Wednesday night, charging documents say, Brown confessed to the crime when questioned by police. He said he and his accomplices had been driving around the city and decided to steal a car. When they came upon Scanlon, they chose her SUV as the target.

Court documents say that Brown admitted pointing a real but unloaded gun at Scanlon to intimidate her. Following his confession, the documents say, Brown wrote Scanlon an apology letter.

Scanlon said she hadn’t seen the letter, but added: “If this is the person who held me up yesterday, they did a very stupid thing, and if their letter of apology is genuine, then it sounds like they can learn from their mistakes.”

Before Wednesday’s carjacking, Brown had been a suspect in several other incidents up and down the I-95 corridor in recent years, according to police and court records.

Authorities in Chester County issued an arrest warrant for Brown in March 2021 after his fingerprints matched those identified by police in a string of vehicle break-ins in Kennett Square in late 2020, police said.

Ten days after that warrant was issued, Brown was picked up by sheriffs deputies in Cecil County, Md., after they responded to reports of car thefts and gunshots. The officers later discovered Brown and six juveniles, at least two of whom were also from Wilmington, inside a vehicle that had been reported stolen in New Jersey.

Police said the vehicle appeared to have been recently struck by gunfire, and two teenage girls inside were suffering from gunshot wounds. They were both hospitalized.

Brown, meanwhile, was arrested on the outstanding warrant from Chester County. He was later released on bail and had been scheduled to stand trial earlier this month on charges including receiving stolen property and theft from a motor vehicle. But the case was delayed, according to court records, which did not provide a reason for the postponement. The case is still listed as active.

As for the teens that were arrested with Brown Wednesday night, none had been charged with participating in the carjacking.

Three of the other teens — boys ages 13 and 16, as well as a 14-year-old girl — were charged in Delaware with receiving stolen property and released to their guardians on $1,500 unsecured bond, police said.

A 15-year-old boy was charged with receiving stolen property, resisting arrest, and two counts of criminal mischief, police said. Police said he was taken to the New Castle County Detention Center on $3,500 bond.