"A girl just shot herself," he told a 911 operator in a call from a restaurant nearby.
Sheldon took the stand Tuesday and the 911 recording was played for the jury at the murder trial of sniper suspect John Allen Muhammad.
Muhammad and Lee Boyd Malvo are accused in the sniper attacks that killed 10 people and terrorized the Washington area for three weeks last year.
Muhammad, 42, is on trial in only one of the killings, the shooting of Dean Harold Meyers at a gas station in Manassas, Va. But prosecutors are presenting evidence from the other shootings, because they must prove multiple killings to convict Muhammad on one of the death-penalty charges against him.
Sheldon testified about the shooting of 34-year-old Sarah Ramos outside a shopping center in Montgomery County.
The retiree testified in a shaky voice that he was putting a letter in a mailbox when he heard "a huge explosion," turned and saw Ramos' bloodied body on the bench. Just moments before, Sheldon had seen a "pretty lady sitting there."
Cynthia Martin, the first police officer on the scene, testified that she could tell immediately that Ramos' wound was not self-inflicted because there was no weapon nearby. Martin also knew there was no way the woman could survive: "When I walked up, her brain was on the ground, had fallen through the bench."
Ramos was one of five people to die in Montgomery County, Md., within a 16-hour period on Oct. 2-3, 2002.
Prosecutors also presented testimony Tuesday in two other fatal shootings on Oct. 3.
Lori Lewis-Rivera, 25, was shot in the back at a Kensington, Md., gas station while she vacuumed her car. Firefighter Steve Steinberg and police officer Terry Ridgely described a chaotic scene, with more than a dozen people gathered around the victim as blood bubbled out of her mouth and nose.
"I felt like a sitting duck out there," Ridgely testified.
Burnell Irby, a high school football coach, testified that later that night, as he headed to a coin laundry in Washington to wash uniforms, he parked his car, got out, heard a pop and saw a flash of light.
Then he heard a woman scream, "Somebody's been shot!" and he realized that the victim was a man who had just walked in front of his car with a rolled-up newspaper under his arm, he said.
The man was 72-year-old Pascal Charlot, a retired carpenter and immigrant from Haiti.
Irby said he thought Charlot was still alive because he had a grimace on his face and the body was moving. "It was just a little bit of movement," Irby said, touching his hand to his chest to demonstrate.
A police officer testified he stopped Muhammad for a traffic violation about two hours before Charlot was shot. Officer Henry Gallagher Jr. said he saw a dark blue Chevrolet Caprice with tinted windows go through two stop signs.
"I thought that a little bit surprising because I was behind him" in a police cruiser, Gallagher said. "I felt he was trying to get away from me."
When Gallagher asked the driver if he had any reason for running the stop signs, a courteous Muhammad replied, "No, sir," the officer testified. Muhammad was alone in the car, he said.
Gallagher said he verified that Muhammad's driver's license was valid and let him go with a verbal warning. Only much later did he learn that Muhammad was a suspect in the shootings.
The stop marked one of several encounters that law enforcement had with Muhammad during the spree, but the manhunt at the time was focused on a white van thought to be the sniper vehicle.
Malvo, 18, goes on trial separately next month in the slaying of an FBI analyst.