The first image the nation saw of the two brothers may serve as more than a pivotal clue to investigators in the Boston Marathon bombings. It is, perhaps, a snapshot of their relationship: One leads, the other follows.
That's how some friends remember the Tsarnaev brothers: At 26, Tamerlan was seven years older than his brother Dzhokhar, who followed his big brother around like a puppy.
And with their father in Russia, the older brother may have become a father figure to the 19-year-old these past few months. At 6-feet-3, Tamerlan was, by many accounts, an intimidating presence with increasingly strong convictions about society and religion in recent years.
But the picture that is emerging of the now infamous brothers is also fuzzy -- just like the surveillance video.
An investigator who studied their video images after the bombings said the two brothers "acted differently than everyone else" -- they stuck around and watched the carnage unfold, and walked away "pretty casually."
Aquaintances of the brothers, now dredging their memories, find themselves short on clues. Many say both were likable and well-loved in their neighborhood, not loners driven away by society.
The casual air of the brothers seemed to mean nothing before Monday, April 15.
'He was a big friendly giant'
Luis Vasquez had planned to watch the finish of the race with his family, but the hectic pace of raising two young children altered his plans.
Vasquez had been friends with Tamerlan and one of his sisters in high school. They would hang out together at cafes and talk about boxing, Tamerlan's real passion. Vasquez also coached the younger brother in soccer at Cambridge Rindge & Latin School.
Reflecting on what transpired this week, he can't help but think of the what-ifs. What if he had attended the marathon? "I wonder if they had seen us ... if they would say anything to us or if they would've acknowledged us in any way," Vasquez said. "That kills me to know, because we were going to be there."
As the oldest of four, Tamerlan seemed to see it as his duty to make sure his siblings didn't forget their Chechen roots. He was about 16 when the family arrived in America.
One sister had an arranged marriage awaiting her in Chechnya, Vasquez said, and "he felt the responsibility to make sure she stayed in line with that." That sister enjoyed the freedom of America, and Tamerlan had "an issue with that." He was like a shadow, always lurking in her presence.
"There was pressure to stick to your ways, your religion, your culture -- to respect that," said Vasquez.
But he saw no seeds of terror.
"He was a big friendly giant. ... There was nothing weird about him, nothing alarming," Vasquez said. "He never went around and tried to force his views on anyone."
Vasquez said he has "very positive memories, very positive interactions."
"The crime doesn't fit the memories."
Clearly, if the allegations against the brothers are true, something changed. Vasquez thinks someone must have "got in his (Tamerlan's) ear and he passed that along probably to whoever he could recruit" -- in this case, he believes, the younger brother.
"In what I've seen of their personalities, the brain behind this is the older brother," Vasquez said. "When it comes to the two of them, he would lead and the little brother followed."
The neighborhood in Cambridge where the family lived at 410 Norfolk is a melting pot of America -- a mix of working-class immigrant families and college intellectuals who attend Harvard and MIT.
It's not unusual for immigrants here to return to their homeland after high school. In fact, it's almost a rite of passage. Residents don't think twice when a neighbor travels to their country of origin.
Yet it is on visits back home in recent years, investigators say, that Tamerlan became radicalized. Shortly after returning from a six-month trip last year, he uploaded several videos to his YouTube account, including one of a well-known jihadist.
Back in 2011, according to the FBI, Russia asked the FBI to interview Tamerlan "based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country's region to join unspecified underground groups."
While investigators continue to pore over evidence and documents, those who knew the brothers say their anger over the bombings is compounded by their confusion -- that two nice guys may have taken such a dark turn.