In the minutes that followed, there was a confrontation with an officer causing Erb to draw and shoot his weapon inside the bus.
Passengers on board ducking for cover, fearing for their lives, and eventually running to safety.
As police began bracing themselves for cover, Erb then approaches the bus' side door with guns in both hands, firing shots to his left and his right as if in an old Western.
Four officers shot back. The officers were identified as First Class officers Carver, Leary, and Minton. The fourth officer's name was held for the officer's duty assignment.
"You heard the first bullet hit the truck like, *bink*, so my first thought is come on get out the truck, get out the truck. We get out of the truck and all you hear is them open fire and shooting everywhere, you see all of the bus people running everywhere," a witness told ABC2 News minutes after the shooting.
After an exchange of gunfire that lasted for minutes, Erb was dead.
But not before shooting and injuring a county police officer, only identified as Officer Slocum, and a 21-year-old bystander.
Both women were sent to the hospital for their injuries.
Baltimore County's State's Attorney said the four officers who fired at Erb were justified in their actions and because there are no charges pending for the officers, a video glimpse into the scary moments of that day.