Top level officials from the Justice Department, FBI, ATF, Department of Homeland Security, Massachusetts State Police and Boston Police Department debated whether they should go public with the images they had found.
By 5 p.m. Thursday, after several delayed news briefings, a task force of federal, state and city law enforcement officials released photographs of the man in the black cap and hoodie and the man in the white cap. They asked for the public's help in identifying them.
"We are processing all the digital photographic evidence we can," Agent Richard DesLauriers, who leads the FBI's Boston division, told reporters. He asked the public to keep submitting their photos to police, noting that investigators had "a huge amount of video evidence to process."
Later that evening, an image of one of the brothers was captured on surveillance video at a convenience store in Cambridge. Then, about 11 p.m., police learned that Sean Collier, a police officer at the Massachusetts Institute of Technology, had been ambushed and shot to death in his patrol car on the campus.
In the early hours of Friday, the pair allegedly carjacked a Mercedez-Benz SUV in Boston, forced the driver to withdraw cash at an ATM, then let him go at a gas station.
The driver called 911 and reported that he'd been held up at gunpoint by two men who said they were the marathon bombers. He also said he'd left his cell phone in the car.
Police were able to track the cell phone -- and the car -- to Watertown, just west of Boston.
Just before 1 a.m. Friday, a lone Watertown cop came upon the brothers, who were now driving two cars, police Chief Edward Deveau said. They were armed with guns, pipe bombs and other explosives. Both cars stopped and the brothers leaped out and opened fire before backup could arrive.
Other officers responded to the pinned-down officer's call for help. More than 200 shots were fired in 5 to 10 minutes.
Deveau said the brothers tossed explosives at police, including a homemade pressure-cooker bomb.
The older brother, Tamerlan, walked straight toward the cops but ran out of ammunition. He'd been wounded. An officer tackled him and police were handcuffing him when Dzhokhar tried to escape in the Mercedes. He aimed the car at the officers, who dove out of the way, and he ran over his brother. The Mercedes dragged the older brother down the street as it sped away.
The driver continued to exchange gunfire with police, then jumped out of the SUV and ran into the darkness.
Authorities finally got names to go with the photos and videos when they scanned a fingerprint from the brother left behind, according to The New York Times. He was Tamerlan Tsarnaev, and he was pronounced dead at a hospital. He was wearing explosives and a triggering device.
Police also learned that the Russian government had asked the FBI to check out Tamerlan's connections to radical Islamic groups in 2011. Nothing had come of the investigation.
Boston woke up Friday morning and learned the names of both bombing suspects. The manhunt for Dzhokhar Tsarnaev lasted all day and shut down much of Boston as police asked everyone to stay indoors. Authorities searched door-to-door in Watertown.
Then, in the evening, the request was lifted and authorities got a tip: A Watertown man told police someone was hiding in his boat in the backyard, bleeding. It was their suspect, the Watertown police chief said.
By then, there were a couple thousand police officers at the scene. A thermal image photograph, released Saturday by state police, showed what authorities say was Dzhokhar Tsarnaev lying in the middle of the boat.
"We know you're in there. Come out with your hands up," police demanded over a bullhorn.
Officers spotted Dzhokhar poking through the tarp and used "flash-bangs," devices meant to stun people with a loud noise. They used a robot to pull the tarp off the boat and negotiated with Dzhokhar for about half an hour.
Police, who had no idea whether he had explosives with him, repeatedly told him to stand up and lift his shirt and he eventually complied.
"Once we saw that, we felt comfortable enough to send some officer tactical equipment to grab him and pull him away from the boat," Deveau said.
The Boston Police Department got the last word on Twitter: "CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody."
A few minutes later, a more somber tweet followed as Boston heaved a sigh of relief:
"In our time of rejoicing, let us not forget the families of Martin Richard, Lingzi Ly, Krystle Campbell and Officer Sean Collier."