During his time in office, President Barack Obama has had to play the role of comforter in chief on several tragic occasions.
The moment the second explosion occurred near the finish line at the 117th Boston Marathon. The bomb blasts took the lives of three victims and injured more than 260 others. (April 15, 2013)
President Barack Obama and first lady Michelle Obama arrive for an interfaith healing service at the Cathedral of the Holy Cross in Boston on Thursday for victims of Monday's Boston Marathon explosions. (April 18, 2013)
Twelve people were killed and 50 were being treated at Denver area hospitals after a shooting at a midnight showing of "The Dark Night Rises", the youngest a 3-month-old baby. (July 20, 2012)
President Barack Obama greets Colorado Gov. John Hickenlooper, left, as Aurora Mayor Steve Hogan, back, watches with other dignitaries after Air Force One landed at Buckley Air Force Base in Colorado. (July 22, 2012)
An armed man stands outside the U.S. consulate in Benghazi, Libya, engulfed in flames after a suspected al-Qaida terrorist attack - previously thought to be a mob - that killed four Americans, including the U.S. Ambassador, Chris Stevens.
U.S. President Barack Obama, left, speaks as U.S. Secretary of State Hillary Clinton, right, listens during the Transfer of Remains Ceremony for the return of Ambassador Christopher Stevens and three other Libyan embassy employees at Joint Base Andrews in Joint Base Andrews, Maryland. (September 14, 2012)
Connecticut State Police lead children from Sandy Hook Elementary School in Newtown, Conn. The shooting took the lives of 27 victims. (Dec. 14, 2012)
Emergency personnel use a stretcher to carry a shooting victim outside a shopping center in Tucson, Ariz. where U.S. Rep. Gabrielle Giffords and others were shot as the congresswoman was meeting with constituents. (Jan. 8, 2011)
President Barack Obama and First Lady Michelle Obama attend the memorial event, Together We Thrive: Tucson and America" at the McKale Memorial Center in Tucson, Arizona. Obama is leading a tribute service for the six people who were killed and the 14 wounded in the assassination attempt on congresswoman Gabrielle Giffords, who is fighting for her life in hospital. (Jan. 12, 2011)
West Virginia State Police direct traffic at the entrance to Massey Energy's Upper Big Branch Coal Mine in Montcoal, W.Va. where an explosion took the lives of 29 miners. (April 5, 2010)
President Barack Obama, walks with Linda Davis, the grandmother of deceased miner Cory Davis, during a memorial for the victims of the Upper Branch Mine explosion at the Beckley-Raleigh County Convention Center in Beckley, W.Va. (April 25, 2010)
Nov. 5, 2009: U.S. Army Major and psychiatrist Nidal Malik Hasan, 39, went on a shooting rampage at the Fort Hood Army Base in Fort Hood, Texas, killing 13 people and injuring 32 others before being shot and captured by police.
President Barack Obama speaks at a memorial service at Fort Hood, Texas. (Nov. 10, 2009)