The two, she said, saw where he was arrested.
"You seen all his blood all over the pavement," she said.
It was an aftermath of an arrest on May 29, 2013, that was allegedly so violent that District Attorney Seth Williams on Thursday charged two Philadelphia police officers with aggravated assault, conspiracy and related crimes.
After seeing the blood, Scannapieco began asking questions.
She eventually found surveillance video, at a barber shop-auto detailing business on the block, that would exonerate Rivera and lead to the arrest of the officers who prosecutors say beat him without provocation and then falsely arrested him.
"This type of behavior has absolutely no place in our city, and I will prosecute these two officers to the fullest extent of the law," Williams said.
The accused officers, Kevin Robinson and Sean McKnight, turned themselves in to police Thursday.
Police Commissioner Charles H. Ramsey suspended the officers with intent to dismiss. Before the video of their arrest of Rivera surfaced, the officers' account of what happened had been accepted as fact, Ramsey said.
In hindsight, Ramsey said, the department should have canvassed the area - a step typically taken only when an Internal Affairs complaint has been filed. The department may now review whether it should further investigate arrests that result in injuries, he said.
Ramsey said he pulled Robinson and McKnight from the street after the video was brought to his attention.
In August 2013, as the case shifted focus toward Robinson and McKnight, the charges against Rivera were dropped.
The two officers had told detectives that they had tried to stop Rivera for running a stop sign on his scooter near Seventh and Cambria Streets in Fairhill.
They said Rivera fled when they exited their patrol car. About 10 minutes later, they said, they saw Rivera lose control of his scooter and fall from the bike several blocks away, on North Sixth.
They told investigators that when they caught up with Rivera, he slammed Robinson against a brick wall, "threw elbows" at him, and tried to pull McKnight's baton from his hand.
Those statements, a grand jury decided, were almost entirely false.
The officers did pull Rivera over that night, Williams said Thursday, but he became frightened and fled when they got out of the car with batons in hand.
The officers gave chase, Williams said, but never turned on their lights or sirens.
On the 2700 block of North Sixth, the surveillance camera caught them knocking Rivera from his scooter, then grabbing and hitting him with fists and batons.
The security camera, the grand jury wrote, picked up his agonized screams.
"Although he was moving around on the ground while being struck, he was not resisting the officers or engaging in any aggressive act," the grand jury said.
Rivera was eventually taken to Episcopal Hospital, Williams said, and while he lay in a hospital bed, McKnight and Robinson filed paperwork and gave statements that led to Rivera's arrest on charges of assault and resisting arrest.
Williams said that Rivera had a juvenile record, but that his encounter with McKnight and Robinson was his first arrest as an adult.
"Even if he had been the devil himself, they could not have done what they did to him," Williams said.
Ramsey said McKnight and Robinson "do not represent the majority" of the 6,500 officers on the force.
"But I cannot stand here and say I've got 6,500 police officers that always operate within the framework of the law, within the framework of department policy," he said. "We've got to root them out."
Additional charges against the officers include recklessly endangering another person, tampering with public records or information, false reports to law enforcement authorities, obstructing administration of law, and official oppression.
John McNesby, president of Lodge 5 of the Fraternal Order of Police, could not be reached for comment Thursday.
Rivera filed a federal civil rights lawsuit against the city Jan. 21. His lawyer, Leo M. Flynn, said the city had already agreed to pay a settlement. Williams said Rivera had settled with the city for $200,000.
Rivera has struggled to move on since.
"I feel like I ain't the same person," he said Thursday night. He suffers from migraines and is forgetful, and his vision is not what it used to be, he says.
"Every time I get next to a cop or a cop is behind me, I get a little panic attack," he said. "And it's sad, because every cop ain't bad."
He said he lost his housekeeping job at Children's Hospital of Philadelphia after the arrest and has not worked since.
Flynn said that without the video, Rivera would have had little chance challenging the testimony of two police officers.
In 2012, Robinson was named a defendant in a lawsuit that alleged he had beaten Darren Trammell, 28, during a trumped-up arrest. Trammell suffered a fractured orbital bone, lacerations, and other injuries, the suit said.
A day after his arrest, Tramell reported the incident to Internal Affairs, which cleared Robinson.
Tramell was eventually cleared of the criminal charges against him. The city settled the case in December for $125,000, according to his lawyer, Andrew D. Swain.
Public Defender Bradley S. Bridge said that because of the criminal charges against Robinson and McKnight, his office will begin reviewing the arrests they made in the past. Since 1995, his office has persuaded judges to overturn more than 500 criminal cases involving Philadelphia police officers who were later arrested on corruption charges.
Ramsey told reporters Thursday that the incident was "a bad case - no doubt about it," but he said the officers' conduct did not mean "every case is tainted."
The charges against Robinson and McKnight come one day after two former police officers were sentenced to prison for corruption, one of them for 17 years.
"It has not been easy for our department this week," Ramsey said.
Still, he said, "every one of these people who get removed from our department brings us a step closer to having the kind of police department that people in this city deserves."