Thursday evening, police released to the public photographs of the brothers made from images captured by security cameras near the marathon finish line on Boylston Street.
Authorities encountered the two bombing suspects for the first time early Friday at the start of what turned into a short, but intense series of violent acts that began with the coincidental robbery of a convenience store in Cambridge. Authorities said Friday that reports the brothers were responsible for the robbery are untrue.
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Watertown, MA, USA
Davis called Collier's death, as he sat in his patrol car, "an assassination."
The brothers are also accused of stealing a car in Cambridge. The car jacking set off a high speed police chase and gun fight that resulted in the elder brother's death. During the chase, the brothers are accused of tossing what are believed to have been homemade pipe bombs at pursuing police officers.
Massachusetts State Police Col. Timothy P. Alben said that Tsarnaev escaped on foot, when the chase ended on the east side of the Watertown. Massachusetts Gov. Deval Patrick said more than 200 shots were fired during the chase.
Friday evening, expressing frustration after hours of intensive but fruitless searching, Alben said, "I believe he is still in Massachusetts. All of his ties are here."
Earlier Friday, an army of state, local and federal police officers closed down Watertown, while searching three quarters of the homes. Authorities also sent police and national guardsman by bus and helicopter to the UMass Dartmouth campus.
The campus was evacuated Friday after several students reported seeing Tsarnaev after the marathon bombing. Students reported that he used the school fitness center on Tuesday and was seen at the off-campus housing complex on Wednesday.
Several students said that they had been interviewed by authorities for periods of as long as five hours Friday.
"I felt safe going here until today," UMass Dartmouth student Mercy Irungu said. "I guess you never know who you go to school with."
She said students received emails from school administrators Friday announcing first that the school was being closed and later that it was being evacuated so authorities could search for bombs. She said students hastily packed clothes and some were bused to a remote location to await rides home from friends and family.
In the Boston area, authorities had restricted air traffic, closed streets, stopped mass transit and persuaded many businesses not to open.
"Be patient," Boston Mayor Thomas Menino said. "We're gonna get through this, we'll be a stronger city as we move forward."
At times Friday, the dragnet spilled over the Massachusetts border.
Heavily armed police in Connecticut boarded a Boston to New York Amtrak train in Norwalk and made a car-by-car search after receiving a report that a passenger resembling Tsarnaev was aboard. The report proved groundless, but all Amtrak service from Boston was stopped for the rest of the day.
Connecticut state troopers were stationed on I-84 at the border with Massachusetts after receiving at least two reports, later proved false, that Tsarnaev had obtained automobiles and may have been attempting to drive out of Massachusetts.
Connecticut State Police also sent explosives experts to Massachusetts to assist in the search for bombs and the disarmament of the pipe bombs the two brothers had flung at police during the car chase in Watertown.
Even members of Tsarnaev's family weighed in on the search. The brothers are ethnic Chechens who appeared to acquaintances to have adjusted well after immigrating with their family a decade ago from Kyrgyzstan, a former republic riven by ethnic and religious strive after the collapse of the Soviet Union. Tsarnaev was an athlete and student. His older brother was a boxer who had qualified for the Golden Gloves national tournament.
But an uncle, Suslan Tsarni, said he believes the young men suffered from a discontent not noticed by casual acquaintances in Massachusetts.
"If you are alive, turn yourself in, and ask for forgiveness from the victims, the injured and from those who are left," Tsarni, told reporters at a news conference outside his home in Montgomery Village, Md.
"You have put shame on this family and on the entire ethnicity" of Chechen, Tsarni said.
"This has nothing to do with Chechnya," Tsarni said. The family is Muslim but the actions of his nephews have nothing to do with that religion either, he said.
"Of course we are ashamed," he said.
By Friday evening, after a series of exhaustive searches for Tsarnaev had proven fruitless, authorities had begun to ease restrictions on movement that for most of the day had given New England's biggest city and many of its densely populated suburbs the appearance of ghost towns.
Police officers across Massachusetts were expressing relief at Tsarnaev's apprehension Friday.
"I wouldn't want to see any police department go through what we went through the last 24 hours," Watertown Police Chief Edward P. Deveau said. "I want to say how proud I am of the people of Watertown. We asked you to be vigilant and we got that call and we got the guy."
U.S. Attorney Carmen Ortiz, whose office is expected to prosecute the case, said it was too early to say whether she will seek a death sentence. She said a tremendous amount of evidence must be evaluated and reviewed before she can determine what charge she will file.
Courant staff writer Dave Altimari and Kelly Glista contributed to this story.A Bloomberg News report is also included.