In the tight rows of chairs in the Commonwealth Ballroom, the nervousness — already dialed high by two bombs, three deaths and more than 72 hours without answers — ratcheted even higher.
The minutes ticked by as investigators stepped out to delay the news conference twice. Finally, at 5:10 p.m. Thursday, a pair of FBI agents carried in two easels and saddled them with display boards, turning the boards backward so as not to divulge the results of their sleuthing just yet.
Now the time had come to take that critical, but perilous step: introducing Boston to the two men believed responsible for an entire city's terror.
"Somebody out there knows these individuals as friends, neighbors, co-workers or family members of the suspects," said Richard DesLauriers, the FBI agent in charge in Boston. As he spoke, investigators flipped the boards around to reveal surveillance-camera images of two men in ball caps.
News cameras pushed forward. Across the city, and across the country, so many people logged on to examine the faces of the men deemed responsible for the bombing attack of the Boston Marathon, that the FBI servers were instantly overwhelmed.
At the least, Bostonians told each other, the photos proved that the monsters the city had imagined were responsible for maiming more than 170 were ordinary men. But even as that relief sank in, the dread that had gripped the city since Monday at 2:50 p.m. was renewed.
If everyone had seen these photos, then that had to mean the suspects had seen them, too.
What desperation might they resort to, marathoner Meredith Saillant asked herself, once they were confronted with the certainty that their hours of anonymity were running out?
On the morning after the marathon, Saillant had fled the city for Vermont, trying to escape nightmares of the bombs that had detonated on the sidewalk just below the room where she'd been celebrating her 3:38 finish. Now, on a smart phone she scrutinized the men's photos.
"I expected that I would feel relief, 'OK, now I can put a face to it,' and start some closure," Saillant says. "But I think I felt more doom. I felt, I don't know, chilled. Knowing where we are and the era in which we live, I knew that as soon as those pictures went up that it was over, that something was going to happen ... like it was the beginning of the end."
There was no way she or the people of Boston could know, though, just when that end would come — or how.
Marathon Monday dawned with an April chill, ideal for keeping a body cool over 26.2 miles. By the four-hour mark, more than two-thirds of the field's 23,000 runners had crossed the finish line.
Passing the 25-mile mark, Diane Jones-Bolton, 51, of Nashville, Tenn., picked up the pace, relishing the sense of accomplishment of her 195th marathon.
Near the finish line, Brighid Wall of Duxbury, Mass., stood to watch the race with her husband and children.
In the post-race chute Tracy Eaves, from Niles, Mich., proudly claimed her medal and a Mylar blanket, and took a big swig from a bottle of Gatorade.
But the blast brought the celebration crashing down.
"Everyone sort of froze...," Wall said. "The first explosion was far enough away that we only saw smoke." Then the second bomb exploded, this time just 10 feet away.
"My husband threw our kids to the ground and lay on top of them," Wall said. "A man lay on top of us and said, 'Don't get up! Don't get up!' "
From her spot beyond the finish, a "huge shaking boom" washed over Eaves.
"I turned around and saw this monstrous smoke," she said. She thought it might be part of the festivities, until the second blast and volunteers began rushing the runners from the scene.
"Then you start to panic," she said.
Back in the field, Jones-Bolton noticed runners turning around and coming back at her. Suddenly the race came to halt, but nobody could say why. When word began to spread, Jones-Bolton panicked at the thought of her husband at the finish line, but was reassured by other runners.
At the finish, Wall, her husband and children raised their heads after a minute or two of silence. Beside them, a man was kneeling, looking dazed, blood dripping from his head. A body lay nearby.
"We grabbed each other and we ran" — into a coffee shop, out the back door into an alley, where they kept going.
Meanwhile, the instincts of Dr. Martin Levine, a Bayonne, N.J., physician who has long volunteered to attend to elite runners at the finish line, told him to do just the opposite.
"Make room for casualties — about 40!," he yelled into the runners' relief tent. Just then the second bomb went off. He reached the site to find a landscape resembling a battlefield, littered with severed limbs.
"The people were still smoking, their skin and their clothes were burning," he said.
Now, three days after the bombing, investigators had made significant headway.
Armies of white-suited agents had sifted through the evidence littering Boylston Street. Their efforts revealed that the bombers had constructed crudely assembled weapons, using plans easily found on the Internet, from pressure cookers, wires and batteries. But investigators still did not know why — or whom to hold responsible.
It all came down to the photos, culled from hundreds of hours of videotape and photographs gathered from surveillance cameras and spectators. But if they were unable to identify the men, that left the investigators with a difficult choice: They could keep them to law enforcement officers, prolonging the search and risking letting the men slip away or attack again. Or they could ask the public for help. But then, the suspects would know the net was closing in.
When they decided to release them, it would only put Bostonians further on edge.
But as investigators pored over tips in the hours before the photos were made public, the city, at least, was struggling to right itself.
On Thursday, President Barack Obama spoke at an interfaith service honoring the victims, saying, "We may be momentarily knocked off our feet. But we'll pick ourselves up. We'll keep going. We will finish the race."
Less than a mile away, 85-year-old Mary O'Kane strained at the bell ropes in the steeple of Arlington Street Church, imagining the sounds spreading healing across her city — and the land.
The city's response to the bombing had revealed its strength. But her belief in Boston was tinged with sadness. Now she understood a bit about how New Yorkers who experienced 9/11 must feel.
"We were feeling sort of immune," she said. "Now we're just a part of everybody...The same expectations and fears."
In the hours after investigators released the photos of the men known only as Suspect (hash)1 and Suspect (hash)2, the city went on about the business of a Thursday night, a semblance of normality restored except for the area immediately surrounding the blast site.
But across the Charles River in Cambridge, Tamerlan Tsarnaev, 26, and his brother Dzhokhar, 19, were busy.
Later, friends and relatives would recall both as seemingly incapable of terrorism. The brothers were part of an ethnic Chechen family that came to the U.S. in 2002, after fleeing troubles in Kyrgyzstan and then Dagestan, a predominantly Muslim republic in Russia's North Caucasus. They settled in Cambridge, where the father, Anzor Tsarnaev, opened an auto shop.
Dzhokhar did well enough in his studies at prestigious Cambridge Rindge and Latin to merit a $2,500 city scholarship for college.
Tamerlan, though, could be argumentative and sullen. "I don't have a single American friend," he said in an interview for a photo essay on boxing. A former accounting student with a wife and daughter, he explained his decision to drop out of school by telling a relative, "I'm in God's business."
For several years Tamerlan had impressed coaches and others as a particularly talented amateur boxer.
"He moved like a gazelle. He could punch like a mule," said Tom Lee, president of the South Boston Boxing Club, where he trained.
But away from the gym, Tamerlan swaggered at times, those who knew him said. And he began declaring an allegiance to Islam, joined with increasingly inflammatory views.
A neighbor, Albrecht Ammon, recalled the older brother arguing with him about U.S. foreign policy, the wars in Afghanistan and Iraq, and religion. The Bible, Tamerlan told him, was a "cheap copy" of the Quran, used to justify wars with other countries. "He had nothing against the American people," Ammon said. "He had something against the American government."
Dzhokhar, on the other hand, was "real cool," Ammon said. "A chill guy."
But after the bombing, when he stopped by a Cambridge auto garage, the mechanic, accustomed to long talks with Dzhokhar, noticed the normally relaxed 19-year-old was biting his nails and trembling.
The mechanic, Gilberto Junior, told Tsarnaev he hadn't had a chance to work on a Mercedes he'd dropped off for bumper work. "I don't care. I don't care. I need the car right now," Junior says Dzhokhar Tsarnaev told him.
Now, with the photos out, it was time to move.
The call to the police dispatcher came in at 10:20 p.m. Thursday: shots fired on the Massachusetts Institute of Technology campus in Cambridge. When police arrived to investigate, they found university officer Sean Collier shot multiple times inside his cruiser.
Witnesses reported seeing two men. Fifteen minutes later, another call came in of an armed carjacking by two men. For the next half-hour, the carjacking victim was kept in his car, had his bank card used to pocket $800 from an ATM and was told by his captors that they'd just killed a police officer and were responsible for the bombing, Watertown Police Chief Edward Deveau said. When the captors went into a Cambridge gas station, the man escaped and called police, said Cambridge Police Commissioner Robert Haas.
Investigators had their break.
Although police had previously said the carjacking victim had left his cellphone in the Mercedes SUV, enabling police to track its location via GPS, Haas said Sunday the phone was found on Memorial Drive near the gas station. It was past 11 p.m. now, and as the Mercedes sped west into Watertown, one of Deveau's officers spotted it and gave chase, realizing too late he was alone against the brothers driving two separate cars. When both vehicles came to a halt, Deveau said, the men stepped out and opened fire. More officers arrived, and when a Massachusetts Bay Transportation Authority officer, Richard Donohue, pulled up behind them, a bullet to the groin severed an artery and he went down.
"We're in a gunfight, a serious gunfight," Deveau said. "Rounds are going and then all of the sudden they see something being thrown at them and there's a huge explosion."
Watertown residents rushed to their windows.
"Now I know what it must be like to be in a war zone, like Iraq or Afghanistan," said 70-year-old Anna Lanzo.
As the firefight continued, Tamerlan Tsarnaev moved closer to the officers, continuing to shoot even as he was hit by police gunfire, until finally he ran out of ammunition and officers tackled him. But as they struggled to cuff the older brother, Dzhokhar Tsarnaev jumped back in the second vehicle, Deveau said.
"Somebody yelled, 'Get out of the way!' and they (the officers) look up and here comes the black SUV that's been hijacked right at them. They dove out of the way at the last second and he ran over his brother, dragged him down the street and then fled," he said.
Tamerlan Tsarnaev was rushed to a hospital, where he was pronounced dead.
But after all the gunfire, the second gunman had vanished. Officers, their guns drawn, cordoned off the area.
At 8:30 a.m., Jonathan Peck heard helicopters circling above his house on Cypress Street and looked outside to see about 50 armed men.
"It seemed like Special Forces teams were searching every nook and cranny of my yard," he said.
Unable to find the second suspect, authorities announced they were shutting down not just Watertown, but all of Boston and many of its suburbs, affecting more than 1 million people. Train service was cancelled. Taxis were ordered off the streets.
But as the hours went by Friday, and the house-to-house search continued, investigators found no sign of their quarry. Finally, at about 6:30 p.m., they announced the shutdown had been lifted.
Across Watertown, people ventured out — including a man who took a few steps into his Franklin Street backyard, then noticed the tarp on his boat was askew. He lifted it, looked inside and saw a man covered in blood.
He rushed back in to call police. Again, the neighborhood was awash in officers. The man hunkered down inside the boat, later identified as Dzhokhar Tsarnaev, traded fire with police for more than an hour, until at last they were able to subdue him.
Around 8:45 p.m., police scanners crackled:
"Suspect in custody."
Bostonians applauded police officers and cheered as the ambulance carrying Tsarnaev passed.
But on Boylston Street, where the bombing site remained cordoned off, tears were shed.
"I think it's a mixture of happiness and relief," said Matt Taylor, 39.
Attorney Beth Lloyd-Jones, who was 25 blocks from the bombings, was planning her wedding inside the Boston Public Library, adjacent to where the bombs exploded.
"Now I feel a little safer," she said. But she couldn't help but think of the victims: "That could have been any one of us."
EDITOR'S NOTE — This reconstruction of events is based on reporting and interviews by Associated Press journalists across Boston and elsewhere from Monday through Saturday. AP writers Bridget Murphy, Michael Hill, Allen G. Breed, Denise Lavoie, Jeff Donn, Meghan Barr, Jay Lindsay, Katie Zezima, Pat Eaton-Robb, Rodrique Ngowi, Bob Salsberg, Marilynn Marchione, and Geoff Mulvihill in Boston; Michelle Smith in Providence, R.I., Michael Rubinkam in Scranton, Pa.; and Trenton Daniel in Port-au-Prince, Haiti, contributed to this report. Follow Adam Geller on Twitter at http://twitter.com/AdGeller