In Massachusetts, the hunt is on

They walked toward the finish line, two brothers, one in front of the other. The eldest, 26-year-old Tamerlan Tsarnaev, led the way, dressed in khaki pants and a V-neck T-shirt. Dzhokhar, just 19, followed a few steps behind, his white baseball cap flipped backward, covering a head of shaggy black hair. Both carried a knapsack.

On Thursday night—just 72 hours after twin explosions rocked the Boston Marathon, killing three spectators and grievously wounding many more—investigators had no idea who those men were. They were prime but unidentified suspects, nameless faces captured on camera in the moments before the blasts. Desperate for a lead, the FBI released their photos to the world.

“In an instant these images will be delivered directly into the hands of millions,” said Special Agent Richard DesLauriers, head of Boston’s FBI field office. “Somebody out there knows these individuals as friends, neighbours, co-workers, or family members.”

Within hours, their cover was blown—and the hunt was on.

At the Massachusetts Institute of Technology, a campus police officer was shot and killed. Minutes later, the two brothers carjacked a Mercedes SUV and led police on a violent, chaotic chase. Though not confirmed, it appeared that explosive devices were thrown from the car.

When it was over, the eldest brother was critically injured, riddled with bullets. He was pronounced dead at hospital. His younger sibling—a “true angel,” according to their shocked father—was still on the lam as of late Friday morning.

As the manhunt intensified, the entire city of Boston was a virtual ghost town. Schools, businesses and all transit lines were ordered closed, and Massachusetts Gov. Deval Patrick implored residents to “stay indoors with the doors locked.”

• The social media trail of the Tsarnaev brothers
• “Turn yourself in,” urges uncle of suspect
• ‘Shots outside my window’

“We believe this to be a terrorist,” said Boston police Commissioner Ed Davis. “We believe this to be a man who’s come here to kill people.”

What motivated these men—immigrants of Chechen origin who had lived in the U.S. for at least seven years—is sure to surface in the hours and days to come. But those who knew them, especially the youngest, were shocked to hear about his connection to such carnage. Dzhokhar was a high school wrestling star, captain of the squad, and was enrolled at the University of Massachusetts at Dartmouth. That campus, too, was closed on Friday. (The city of Cambridge, where he apparently lived, had awarded him a $2,500 scholarship.)

On Vkontakte, a popular social media site, Dzhokhar described his world view as “Islam.” Asked to identify “the main thing in life,” he answered “career and money.” Later in the post, he listed a verse from the Koran: “Do good, because Allah loves those who do good.”

His older brother also had a significant online presence. His favourite YouTube clips included Russian rap videos and a testimonial from a young ethnic Russian: “How I accepted Islam and became a Shiite.” Another favourite video was “Seven steps to successful prayer.” An engineering student at Bunker Hill Community College, Tamerlan was also an aspiring boxer who apparently dreamed of landing a spot on the U.S. Olympic team. One photo essay posted online shows Tamerlan sparring with an unnamed fighter. “I don’t have a single American friend,” he said, in one photo caption. “I don’t understand them.”

Ruslan Tsarni, the men’s uncle, told reporters outside his home that he hadn’t spoken to his nephews in a couple of years. But on Thursday night, less than two hours after their photos were released, he received a phone call from Tamerlan. “He called me and said: ‘Forgive me,’ ” Tsarni said. “It’s crazy. It’s not possible. I can’t believe it. Myself, when I heard this on the TV news I was thinking: who can do this stuff?”

An aunt, who lives in west-end Toronto, told one reporter that she doesn’t want to believe her nephews are terrorists. “This is a huge tragedy for the family,” said Maret Tsarnaev, 45. “My brother’s two boys, they are growing up so fast. My first reaction is, why the hell would they do this? But when I go through all the material, it’s not giving anything?.?.?.?the whole world is now making a decision [on them] now by just seeing these pictures and not having anything else.”

The aunt told the Toronto Sun she hasn’t seen the men for five years, but knew they were living in Cambridge. Dzhokhar had a love of math and was attending school there. Tamerlan, she said, had a two-year-old daughter. “These two boys, all they must have in their heads at this age is love,” she said. “I cannot believe Tamerlan is dead. This cannot be true.”

The two bombs—crude devices believed to be made of pressure cookers stuffed with nails, ball bearings another projectiles—detonated 12 seconds apart, just before 3 p.m. on Monday. Like an improvised explosive device found on the battlefields of Afghanistan, the blasts ripped apart limbs and filled the sidewalks with blood and debris. Among the dead was an eight-year-old boy, Martin Richard, whose mother and sister are still recovering in hospital. Krystle Campbell, 29, and Lingzi Lu, a Chinese graduate student studying at Boston University, also perished.

From the outside, the ensuing investigation has appeared disjointed, even bumbling. On Wednesday, numerous news outlets reported that a suspect was in custody and on his way to court—only to retract after the FBI, and other senior U.S. officials, insisted it wasn’t true. But Thursday’s photographic release, barely three days after the tragedy, was proof of the intense, fruitful police work going on behind closed doors. From an investigative standpoint, things could not have moved much faster.

Before the last casualty was even whisked away to a hospital Monday afternoon, forensic teams were on site, sifting through the wreckage and collecting critical bits of evidence. By the very next day, authorities had released unprecedented photographs of the bomb parts found at the crime scene—the kind of images that are typically saved for court. And on Thursday, after poring through thousands of cellphone photos and surveillance clips, investigators had a fairly certain idea of who they needed to find.

By early Friday morning, one was dead. The other is now the most wanted man in the world.