Projections of the Boston Marathon Memorial Ribbon are seen on the ice during pre-game ceremonies in remembrance of the Boston Marathon bombing victims before the first Boston Bruins home game following the attack.

A projection of the Boston Marathon Memorial Ribbon is seen on the ice.

Bruins fans sing the National Anthem during pre-game ceremonies in remembrance of the Boston Marathon bombing victims.

A photograph of Boston University student Lingzi Lu, who was killed in the Boston Marathon explosions, sits on a table as a student writes a message on a board outside the school's Marsh Chapel before a vigil.

The John Joseph Moakley US Courthouse, where a large contingent of media had gathered in anticipation of an appearance by a possible suspect in the bombings, was evacuated Wednesday afternoon because of a bomb threat.

Pictured: Employees gathered outside the courthouse after being evacuated.

Federal Protective Service and court security officers communicated outside the courthouse.

A bomb sniffing dog was brought around the perimeter of the courthouse.

A crowd of journalists and people who were evacuated from the courthouse stood in a nearby parking lot.

Security officials guarded the courthouse.

FBI investigators checked for evidence under portable toilets on Clarendon Street.

Officials took crime scene photos on Wednessday, two days after two explosions hit the Boston Marathon. The investigation of the Boston Marathon bombing is focusing on a suspect or suspects believed to have carried heavy bags or backpacks, but entered a third day on Wednesday without any arrests or word on who was responsible.

Items began to build at a memorial for Boston University Graduate student Lu Lingzi at the base of the Martin Luther King Jr. memorial outside the Marsh Chapel on the university's campus as an investigation continues into dual bombings at the Boston Marathon finish line.

A sign hangs on a barricade to Boylston Street at Berkeley Street.

Patty Campbell, mother of Krystle Campbell, spoke Tuesday from her front porch flanked by her brother John Reilly and son Billy Campbell. Krystle died in the bomb attack at the Boston Marathon.

Boston police officer Pat Duggan wrote in chalk outside a makeshift memorial along Newbury street.

This image from a Federal Bureau of Investigation and Department of Homeland Security shows the remains of a black backpack that the FBI said contained one of the bombs that exploded during the Boston Marathon.

This image from a Federal Bureau of Investigation and Department of Homeland Security shows the remains of a pressure cooker that the FBI said was part of one of the bombs that exploded during the Boston Marathon.

People held patriotic balloons as they stood on a portion of Boylston Street which was reopened a day after the two explosions.

A police SWAT team patrolled the streets in the vicinity of the Boston Marathon as an investigation continues into dual bombings at the site in Boston.

National Guard and Boston police man a barricade in front of the medical tent near the finish line in Boston Tuesday, April 16, 2013 where some of the wounded were treated in yesterday's explosions at the Boston Marathon. (AP Photo/Winslow Townson)

A woman places flowers at a barricade which has become a memorial site on Boylston Street.

BOSTON—APRIL 16: Investigators in white jumpsuits work the crime scene on Boylston Street following yesterday's bomb attack at the Boston Marathon April 16, 2013 in Boston, Massachusetts. Security is tight in the City of Boston following yesterday's two bomb explosions near the finish line of the Boston Marathon, that killed three people and wounding hundreds more. (Photo by Darren McCollester/Getty Images)

People in hazardous materials suits investigate the scene at the first bombing on Boylston Street in Boston Tuesday, April 16, 2013 near the finish line of the 2013 Boston Marathon, a day after two blasts killed three and injured over 170 people. The bombs that ripped through the Boston Marathon crowd were fashioned out of ordinary kitchen pressure cookers, packed with nails and other fiendishly lethal shrapnel, and hidden in duffel bags left on the ground, people close to the investigation said Tuesday. (AP Photo/Elise Amendola)

BOSTON—APRIL 16: (EDITORS NOTE: Retransmission with alternate crop; Best quality available) Investigators in white jumpsuits work the crime scene on Boylston Street following yesterday's bomb attack at the Boston Marathon April 16, 2013 in Boston, Massachusetts. Security is tight in the City of Boston following yesterday's two bomb explosions near the finish line of the Boston Marathon, that killed three people and wounding hundreds more. (Photo by Darren McCollester/Getty Images)

Men in hazardous materials suits put numbers on the shattered glass and debris as they investigate the scene at the first bombing on Boylston Street in Boston Tuesday, April 16, 2013 near the finish line of the 2013 Boston Marathon, a day after two blasts killed three and injured over 170 people. The bombs that ripped through the Boston Marathon crowd were fashioned out of ordinary kitchen pressure cookers, packed with nails and other fiendishly lethal shrapnel, and hidden in duffel bags left on the ground, people close to the investigation said Tuesday. (AP Photo/Elise Amendola)

Two men in hazardous materials suits put numbers on the shattered glass and debris as they investigate the scene at the first bombing on Boylston Street in Boston Tuesday, April 16, 2013 near the finish line of the 2013 Boston Marathon, a day after two blasts killed three and injured over 170 people. The bombs that ripped through the Boston Marathon crowd were fashioned out of ordinary kitchen pressure cookers, packed with nails and other fiendishly lethal shrapnel, and hidden in duffel bags left on the ground, people close to the investigation said Tuesday. (AP Photo/Elise Amendola)

Runners and spectators were immediately evacuated for the area. The MBTA shut down all services and surrounding building were placed on lockdown.

Ayk Oganesyan walked down Newbury Street with friends playing music blocks away from the scene of yesterday's bombing attack.

A Rosary, left, hung from a barricade near a Boston Marathon finisher's medal, center, guarded by a Massachusetts National Guard member near a makeshift memorial on Boylston Street.

Flowers and a card with a touching message were left on the gazebo at Hopkinton Town Green near the race’s starting line.

Jackie (left) and Greg Pavek, 65, of Wisconsin, comforted each other this morning at a Hopkinton restaurant. Jackie Pavek was watching from the VIP stands and her husband was yards from the finish when the explosions took place Monday. Greg Pavek, who has run Boston six times, said he didn’t know if he would participate in another Boston Marathon.

A sign on the Southeast Expressway northbound, at Exit 16 (Andrew Square), was simple and effective in its message.

Massachusetts State Trooper Mike Currier and his dog, Chico, patrolled today in Terminal B at Logan Airport.

Satellite trucks took over Arlington Street near its intersection with Newbury Street.

A Boston Police Department bomb squad vehicle sat on Huntington Avenue today.

A joint command center has been set up on Boston Common.

Claire Winship (left) of Brighton embraced Keith Martin, who advertised free hugs on Boston Common.

An aerial view of Boylston Street, which is closed for blocks in the wake of the explosion.

Amtrak police officer Joe Agnellino and his bomb detection dog Roxy checked passengers before they boarded a train at South Station.

Officials took photos at the crime scene.

Nicholas Yanni, who was injured in the explosions, described the blast and his injuries during a news conference at Tufts Medical Center.

From left, Jim Casey, Liz Norden of Wakefield, and Mike Jefferson comforted each other on Tuesday. Nordon is the mother of two sons who each lost a limb in Monday’s Boston Marathon bombings; the boys were there to watch their brother, Jefferson, a 31-year-old Somerville firefighter who was running in the marathon.

Drs. Alasdair Conn (left) and George Velmahos of Massachusetts General Hospital briefed the media Tuesday on the status of patients injured in the explosions.

Boston College senior Marissa Irwin, a marathoner, left a flower against a police barricade on Boylston Street.

National Guardsmen stood watch on the Orange Line platform at Back Bay Station this morning.

Marathon runners, from left, Tammy Snyder, Diane Deigmann, and Lisa Kresky-Griffin embraced in front of a barricade on Boylston Street.

Investigators used a firetruck's bucket to take aerial photographs of the crime scene at the Boston Marathon finish line.

Governor Deval Patrick spoke at a news conference with Boston Mayor Thomas M. Menino (center) and FBI Special Agent-in-Charge of Boston Richard Deslauriers (left).

The US flag was lowered at the White House to honor the victims of the explosions.

Traders on the floor of the New York Stock Exchange observed a moment of silence today.

Neighbors came to pay their respects at the home of 8-year-old Martin Richard in Dorchester.

Runner Megan Cloke paused after placing flowers on the doorstep of the Richard home in Dorchester today. Martin Richard, 8, was killed in Monday’s bombings at the finish line of the Boston Marathon.

Jacqueline Myers (right) and her 10-year-old daughter, Amira, walked away after leaving a teddy bear on the door step of the Richard home. Amira Myers was a schoolmate of Martin Richard.

Friends of bombing victim Martin Richard created a chalk memorial at a Dorchester playground.

A National Guardsman checked identification at a roadblock near the scene of the explosions.

Unused thermal blankets were piled near the crime scene.

Workers found bags containing runners' personal effects near the finish line.

Newspapers were on sale at a stand on Newbury Street.

A Revere firefighter left the scene after a search of an apartment at 364 Ocean Ave. late Monday.

Investigators left an apartment complex in Revere late Monday.

People reacted after a bombing near the finish line at the Boston Marathon.

People assisted the wounded outside of the Forum restaurant on Boylston Street.

A person's blood stained feet hung outside an ambulance at a medical tent located near the finish line.

A wounded person was rushed from the scene.

A woman was helped from scene on Boylston Street.

A Boston Marathon competitor and Boston police ran from the scene of the bombing near the finish line.

A man in tears was helped from scene on Boylston Street.

A woman looked at the blood on her hands as she was loaded into an ambulance after being injured.

A military police officer stood guard at a staging area located at the Boston Common.

An unidentified Boston Marathon runner was comforted after the blasts.

A member of the bomb squad investigated a suspicious item on the road near Kenmore Square.

Runners were gathered on Commonwealth Avenue near Massachusetts Avenue after the blasts.

Suffolk District Attorney Daniel Conley asked people to move back from the scene following the blasts on Boylston Street.

Police are seen on the roof of a building overlooking Boylston Street where explosions went off .

A State Police officer inspected a suspicious package on Stuart Street.

Volunteers organized participants collecting their belongings.

An armed FBI agent passed a Boston police officer following the blasts.

Boston Police struggled to remove barricades to reach victims of the first explosion.

An injured woman was carried away from the scene.

In this image from video provided by WBZ-TV, spectators and runners run from explosions.

People injured during the bombing were brought to Boston Medical Center.

A Boston police officer carried a young boy outside of the Forum restaurant on Boylston Street.

A woman knelt and prayed at the scene of the first explosion on Boylston Street .

The explosion left this man’s clothes in tatters.

A man was helped on the sidewalk at the scene of the first explosion at the finish line.

President Obama discussed the bombings.

Boston Mayor Thomas M. Menino spoke at press conference. He was surrounded, from left, by US Attorney Carmen Ortiz, Governor Deval Patrick, and US Representative Stephen Lynch.

Marathon runners reacted as emergency response crews worked the scene of the bombing.

An injured man stood at the scene of an explosion.

People assisted an injured man.

An injured woman was helped by a firefighter and a bystander.

Medical workers aided injured people.

A runner sat near Kenmore Square after two bombs exploded.

President Obama spoke on the phone with FBI Director Robert Mueller to receive an update on the bombings in Boston. Seated with Obama were Lisa Monaco, assistant to the president for Homeland Security and Counterterrorism, and Chief of Staff Denis McDonough.

US Representative Stephen Lynch arrived at the Westin Hotel after the bombing.

Women desperate to hear from loved ones were kept away from the bombing scene at Boylston Street and Massachusetts Avenue.

Boston Police looked at blown out windows at the scene of the first explosion on Boylston Street .

Emergency responders comforted a woman on a stretcher who was injured in a bomb blast near the finish line.

A woman reacted to the bombing.

A woman left the vicinity of the Boston Marathon finish line following the bombing.

Medical responders run an injured man past the finish line.

People reacted to a second explosion near the finish line.

The scene on Boylston Street as seen after one of the explosions.

Police and runners reacted to one of explosions.

Bystanders tended to an injured man.

Marathon runners are covered in blankets after the bombing.

Firefighters tended to a man following an explosion at the finish line of the Boston Marathon.

One of the blast sites on Boylston Street near the finish line was investigated by a person in a protective suit in the wake of two blasts.

Bloody clothing and medical pads were found on Commonwealth Avenue in Boston near the scene of multiple explosions at the end of the Boston Marathon finish line.

A Massachusetts State Police trooper guarded the area containing the medical tent.

People on Boylston Street reacted to the explosion.

Katherine Swierk, left, was reunited with her aunt Terry Days, center, and friend Jocelyn Cacio outside Copley Square in Boston after explosions during the Boston Marathon.

Justine Franco of Montpelier, Vt., held up a sign near Copley Square looking for her missing friend, April, who was running in her first Boston Marathon.

Governor Deval Patrick updated the public on the incident during a press conference. Behind him is Boston Police Commissioner Edward F. Davis.

Medical workers wheeled the injured across the finish line during the 2013 Boston Marathon following an explosion.

Medical workers aided injured people at the finish line of the 2013 Boston Marathon following an explosion in Boston.

One of the medical tents was turned into a morgue.

Map of the explosion locations.

Police officers with their guns drawn heard the second explosion down the street. The first explosion knocked down a runner at the finish line of the Boston Marathon.

Explosions blew out windows of Marathon Sports store in Copley Square.

Some of the injured were treated at the Boston Marathon medical tent.

The explosions occurred on Boylston Street near the viewing stands overlooking the finish line.

People were assisted outside of the Boston Public Library.

An injured person was rushed away from the scene.

An injured person was rushed away from the scene.

Rows of ambulances rushed to the scene of the explosion.

Two explosions shattered the euphoria at the Marathon's finish line, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts.

A runner was blown to the ground by the first explosion near the finish line of the Boston Marathon.

Medical workers aided injured people at the finish line of the 2013 Boston Marathon following an explosion in Boston.