![Investigators worked at the scene on Boylston Street, and hundreds of officers fanned out across the city Tuesday.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/tlumacki_bombaftermath0332-4190.r.jpg)
John Tlumacki/Globe Staff
Investigators worked at the scene on Boylston Street, and hundreds of officers fanned out across the city Tuesday.
![Remains of a backpack the FBI says contained one bomb.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/backpack.r.jpg)
ASSOCIATED PRESS
Remains of a backpack the FBI says contained one bomb.
![This image shows the remains of a pressure cooker that the FBI says was part of one of the bombs.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/cooker.r.jpg)
Associated Press
This image shows the remains of a pressure cooker that the FBI says was part of one of the bombs.
![Emily Gillis, 7, her brother Conor, 4, of Dorchester, and their cousin Benjamin McCormick, 8, of Milton attended a vigil for blast victim Martin Richard at Garvey Park in Dorchester.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/130416bombrichard0112-4242.r.jpg)
Yoon S. Byun/globe staff
Emily Gillis, 7, her brother Conor, 4, of Dorchester, and their cousin Benjamin McCormick, 8, of Milton attended a vigil for blast victim Martin Richard at Garvey Park in Dorchester.
![Garvey Park in Dorchester was nearly filled with people during the vigil for Martin Richard, who was killed in Monday's blasts.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/130416bombrichard0168-4252.r.jpg)
Yoon S. Byun/globe staff
Garvey Park in Dorchester was nearly filled with people during the vigil for Martin Richard, who was killed in Monday's blasts.
![Sam Galvin of West Roxbury added candles to a make-shift memorial on the barricades blocking off Boylston Street.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/Boghosian_Bombing18_MET2.r.jpg)
Aram Boghosian for The Boston Globe
Sam Galvin of West Roxbury added candles to a makeshift memorial on the barricades blocking off Boylston Street.
![Sisters Justine Lescarbeau (left) and Jocelyn Lescarbeau, both of Boston, sign a banner during a vigil and memorial on Boston Common.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/suarez_p17bombmainphoto_MET_006_1.r.jpg)
Essdras M. Suarez/Globe Staff
Sisters Justine Lescarbeau (left) and Jocelyn Lescarbeau, both of Boston, sign a banner during a vigil and memorial on Boston Common.
![Lizzie Lee, 56, of Lynwood, Wash., who was participating in her first Boston Marathon, holds a candle and a flower at a vigil at Boston Common.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/vigil1.r.jpg)
Julio Cortez/AP
Lizzie Lee, 56, of Lynwood, Wash., who had participated in her first Boston Marathon, holds a candle and a flower at a vigil at Boston Common.
![Members of the military walked along Boylston Street near the finish line of the Boston Marathon.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/17/BostonGlobe.com/Metro/Images/Boghosian_Bombing20_MET2.r.jpg)
Aram Boghosian for The Boston Globe
Members of the military walked along Boylston Street near the finish line of the Boston Marathon.
![The Red Sox had a moment of silence for victims before a game in Cleveland, playing the Indians at Progressive Field.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Sports/Images/soxmarathon%20(3).r.jpg)
Mark Duncan/AP
The Red Sox had a moment of silence for victims before a game in Cleveland, playing the Indians at Progressive Field.
![Sox second baseman Dustin Pedroia walked past a sign from an Indians fan in the dugout.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Sports/Images/soxmarathon%20(4).r.jpg)
Mark Duncan
Sox second baseman Dustin Pedroia walked past a sign from an Indians fan in the dugout.
![Investigators were combing through the aftermath of the deadly Boston Marathon terrorist attack Tuesday.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/tlumacki_bombaftermath0902-4186.r.jpg)
John Tlumacki/Globe Staff
Investigators were combing through the aftermath of the deadly Boston Marathon terrorist attack Tuesday.
![The scene outside of Marathon Sports, the site of the first bomb explosion.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/aftermath2-4189.r.jpg)
John Tlumacki/Globe Staff
The scene outside of Marathon Sports, the site of the first bomb explosion.
![A woman looked down Boylston Street Tuesday, toward the finish line of the Boston Marathon and the site of deadly bombings a day earlier.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/boylston3-4183.r.jpg)
MATTHEW CAVANAUGH/EPA
A woman looked down Boylston Street Tuesday, toward the finish line of the Boston Marathon and the site of deadly bombings a day earlier.
![A Boston Police officer stood on Boylston Street on Tuesday.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/boylston2.r.jpg)
MATTHEW CAVANAUGH/EPA
A Boston Police officer stood on Boylston Street on Tuesday.
![Boston Police Commissioner Edward Davis spoke along with other local and federal officials Tuesday morning.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/slider_presser2.r.jpg)
Bill Greene/Globe Staff
Boston Police Commissioner Edward Davis spoke along with other local and federal officials Tuesday morning.
![Senator Elizabeth Warren, Boston Mayor Thomas M. Menino, Governor Deval Patrick, and FBI special agent in charge Richard DesLauriers spoke at the press conference.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/slider_bcc78c06595d4fb285d107dd12107db4-bcc78c06595d4fb285d107dd12107db4-0.r.jpg)
Elise Amendola/Associated Press
Senator Elizabeth Warren, Boston Mayor Thomas M. Menino, Governor Deval Patrick, and FBI special agent in charge Richard DesLauriers spoke at the press conference.
![Speaking Tuesday afternoon at the White House, President Obama said,](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/bgcom-16obamapic.r.jpg)
Susan Walsh/Associated Press
Speaking Tuesday afternoon at the White House, President Obama said, "We do not know whether this is an act of an organization, or an individual, or individuals."
![A military police officer checked the identification of a man on Massachusetts Avenue on Tuesday morning.](http://www.bostonglobe.com/rf/image_r/Boston/2011-2020/2013/04/16/BostonGlobe.com/Metro/Images/slider_166729151.r.jpg)
Darren McCollester/Getty Images
A military police officer checked the identification of a man on Massachusetts Avenue on Tuesday morning.