Across the Charles River, several blocks from the shooting scene, a man who authorities believe was Tamerlan Tsarnaev approached a black Mercedes ML 350 SUV in the Allston neighborhood and tapped on the passenger window. The driver rolled down the window and the suspect reached inside, opened the door and brandished his handgun.
"Did you hear about the Boston explosion?" he said, according to an affidavit. "I did that."
He pulled the magazine from his weapon and showed he was loaded. "I am serious," he said.
The driver told the Boston Globe it was the start of a terrifying 90-minute odyssey across metro Boston, first with the younger brother trailing in a second car, before stopping in a neighborhood in East Watertown. It was there, the driver said, the two men transferred heavy objects into the Mercedes.
"Luggage," the driver thought, according to the Globe.
The younger brother, Dzhokhar, hopped in the back seat. Tamerlan took over the driving.
"They asked me where I'm from. I told them I'm Chinese," the carjacking victim told CNN-affiliate WMUR. "I asked them if they were going to hurt me. They said they won't hurt me. I was thinking, 'I think they will kill me later.'"
The man with the gun demanded cash. The carjacking victim handed over $45. They wanted more money so he gave the his ATM card and the passcode. Dzhokhar was seen on surveillance video at a Bank of America ATM at 11:18 p.m.
Both brothers were said to love high-end cars, and now they were in a carjacked Mercedes darting from Allston to Watertown to Cambridge. Eventually, the fuel tank neared empty.
The brothers mentioned something about New York as they drove, according to the driver. Authorities have since said the two planned to attack Times Square.
The Mercedes pulled into a Shell gas station on Memorial Drive. At that time of night, the station only accepted cash to pump gas. Dzhokhar went inside to pay. According to the Boston Globe, Tamerlan put his gun in the door pocket to fiddle with a navigation system.
The carjacking victim saw this as his opportunity to flee. "I jumped out of the car and ran away across the street," he told WMUR.
Tamerlan tried to grab him, "but I ran very fast." He could hear the man swearing as he sprinted for his life.
"It was very scary at that moment," he recalled. "For me, I'm so lucky."
He burst through the door of a nearby Mobil gas station so hard, the clerk was angry -- until he saw the panic on the man's face and heard his pleas to call police. The carjacking victim curled up in a back room and hid.
The men in the stolen SUV sped off.
Somewhere along the way, the two stopped to pick up their other car: a green Honda Civic with a Massachusetts tag 116GC7. Earlier in the day, authorities had put out an all-points bulletin for that exact vehicle.
A dramatic shootout in Watertown
"Heading to Watertown," the voice said over police dispatch.
Two hours had passed since the shooting at MIT. The next hour was followed by a bizarre carjacking.