As Tuesday melted into Wednesday, J_tsar was back on Twitter. "I'm a stress free kind of guy," he tweeted shortly before 2 a.m.
The day seemed like any other at school for the Mercedes-driving 19-year-old later identified as the tweeter: Dzhokhar Tsarnaev, a sophomore at the University of Massachusetts-Dartmouth. His student ID told the story of his day; like all students, he has to swipe the card to enter buildings on campus.
Card swipe information shows he went to the gym and spent Wednesday night at his dorm. Dzhokhar was known as Jahar to friends on campus.
Student Zach Bettencourt said he discussed the bombing with Dzhokhar at the gym.
"You hear about this kind of thing happening in Iraq and Afghanistan but not here," Bettencourt said.
Dzhokhar responded: "Yeah tragedies happen man, like these things happen around the world. It's crazy."
Less than 48 hours after the bombing, Harry Danso was making small talk with Dzhokhar at their dorm. "He was just in the hallway, said 'Hi' and walked past me. He just acted regular. Gave me a regular smile, like usual."
He also went to a party at the dorm, a fellow student told The Boston Globe. It was attended by friends who competed in intramural soccer.
"He was just relaxed," the student said, asking the paper not to publish her name. Also on Wednesday, authorities revealed that one and possibly both of Monday's deadly devices had been fashioned out of pressure cookers. A pressure cooker lid was found on a rooftop near the marathon finish line.
Meanwhile, Dzhokhar's older brother, Tamerlan, was reaching out to family members. He called two uncles on Thursday, seeking their forgiveness.
"He called me, confused," Ruslan Tsarni, who lives outside Washington, told CNN. In an earlier interview with USA Today, another uncle quoted Tamerlan as saying, " 'I love you and forgive me' ... I guess he knew what he had done."
More violence, and a breakthrough
Thursday was a breakthrough day for investigators.
They already had made progress, finding clear images of the men with the backpacks and ball caps on a surveillance video. Intelligence had been developed on one suspect earlier in the week; images of the second suspect were isolated Wednesday, officials told CNN.
Jeff Bauman, who'd survived the bombing but lost both legs, regained consciousness at Boston Medical Center and gave them a lead. On a piece of paper, he wrote: "Bag, saw the guy, looked right at me."
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.