The 19-year-old man wanted in the fatal shooting of a Philadelphia police commander’s son was captured late Wednesday afternoon on the roof of a Delaware County business, a U.S. Marshals Service spokesperson said.

Tyquan Atkinson was apprehended by members of the Marshals Fugitive Task Force shortly before 6 p.m. in the 800 block of Upland Avenue in Upland Borough, said Supervisory Deputy U.S. Marshal Robert Clark.

Deputy marshals and detectives with the Philadelphia Police Department had a house in Chester under surveillance when they spotted Atkinson leaving through the back door, Clark said. Atkinson was tracked down to the rooftop and taken into custody without incident.

Earlier Wednesday, Philadelphia police identified Atkinson, also known as “Fats,” as the suspect they said fired the shot that killed 20-year-old Nicholas Flacco on Saturday night at a postgame Phillies tailgate in FDR Park.

Atkinson’s last known address was in the 1600 block of South 32nd Street. He also was known to frequent the areas of 10th Street and Oregon Avenue, and 12th and Ritner Streets, police said.

At a news conference at Police Headquarters, Homicide Capt. Jason Smith said tips helped lead detectives to identify Atkinson as a suspect in the killing of Flacco, a Pennsylvania State University student and son of Chief Inspector Christopher Flacco. An arrest warrant on murder and related charges was issued Tuesday night, Smith said.

Smith said investigators believe the killing occurred after mounting tensions in the park and fights between two groups of teens and young adults that knew each other — one group from South Philadelphia, another from the Northeast.

Smith declined to elaborate on the source of friction between the groups or to say how they knew each other, but he urged anyone connected to either side to avoid escalating what he called a “volatile” situation as police searched for Atkinson and continued investigating.

Smith said detectives believe that Atkinson had been called to the park by a woman involved in fights that broke out during a lingering tailgate party. He said initial witness interviews described a chaotic scene, with brawls and melees erupting among various groups before 10 p.m.

Smith said investigators believe that Flacco may have tried to break up a fight between women but that he otherwise was not an active participant in the mayhem.

Still, Smith said that after one of the fights, a woman — whom police did not identify — threatened to call “her man” and that she said people should be scared.

A short time later, Smith said, a gunman arrived and fired a shot into the air. Several of Flacco’s friends, apparently believing the weapon was fake, then “dared” the gunman to shoot again, Smith said. He fired another shot that did not hit anyone, then left, Smith said.

Smith did not know whether anyone called police after that encounter, but he said that possibly 10 to 15 minutes later, the gunman returned and fired at Flacco, hitting him in the chest.

Police took Flacco to Penn Presbyterian Medical Center, where he was pronounced dead at 10:17 p.m.

Flacco, in his fourth semester at Penn State, was back in the city to celebrate his 20th birthday on Friday and attend Saturday’s Phillies game against the Atlanta Braves, Police Commissioner Richard Ross said.

He graduated from Holy Ghost Preparatory School in Bensalem in 2017, the school said in a statement. The statement also said that Flacco had hoped to follow in the footsteps of his father and grandfather by becoming a member of the U.S. Marine Corps.

Flacco’s Funeral Mass was scheduled for noon Thursday, according to his obituary.

Staff writer Robert Moran contributed to this article.