Delaware County authorities say "extensive" witness cooperation - a rarity in some sections of Chester - helped them identify a suspect in Monday's shooting of two brothers in Highland Gardens.

Now, they need the public's assistance to apprehend the alleged triggerman.

Angus Richardson, 24, of Upland, was charged yesterday with murdering Otis Bullock, 21, and seriously injuring his brother, Leon Bullock, 19, by opening fire with a shotgun Monday afternoon.

"Unfortunately, at this time, Angus Richardson remains at large," said Delaware County District Attorney G. Michael Green.

Green said that Richardson, who has an active warrant for a domestic incident reported last month, is still believed to be in the Philadelphia area.

He allegedly fired multiple shots at the Bullock brothers and others in their group from a white SUV that stopped on McCarey Street near 10th.

Otis Bullock, who was hit in the chest, was pronounced dead Monday evening.

Leon Bullock remains hospitalized with a severe leg injury from the shotgun blast.

"All of us wish to commend the extensive cooperation we received from individuals in the city of Chester," Green said.

Before the shooting, Green said, the Bullocks and others had traveled to West 21st Street and engaged in a fight with Richardson, apparently over threats Richardson had made toward the Bullocks' sister.

Yesterday's ordeal may have originated from bad blood between Richardson's girlfriend and the Bullocks' sister, police said.

"Angus Richardson should be considered armed and dangerous," Green said.

"Anyone observing Angus Richardson should not approach him."

Tips on Richardson's whereabouts should be directed to Chester Police Detective Randy Bothwell at 610-447-8430, county Detective Michael Jay at 610-891-4700 or Chester City's anonymous tip line at 610-447-7810.