Five days in April: The Boston Marathon bombing and the manhunt that followed

A bomb explodes in the crowd as runners cross the finish line during the 117th Boston Marathon. 

Police officers with their guns drawn react to a second explosion down the street.

The first explosion knocked down the runner at the finish line. 

Bystanders help 17-year-old Sydney Corcoran at the scene of the first explosion on Boylston Street near the finish line.

She survived the blasts.

An emergency responder and volunteers, including Carlos Arredondo in the cowboy hat, push Jeff Bauman in a wheelchair after the explosion near the finish line. 

Bauman lost both his legs in the explosion. His story was told in the 2017 film "Stronger," starring Jake Gyllenhaal. 

An investigator holds the remains of a pressure cooker, used to make a bomb, found at the scene. 

The unfinished meals of fleeing customers are left on tables at an outdoor restaurant the day after the bombing. 

A Boston Police officer lifts the tape for a family to leave flowers in front of the home of the Richard family whose eight-year-old son, Martin, was killed in the blasts.

Investigators work at the scene of one of the blast sites. 

Tamerlan Tsarnaev, in black baseball hat, and his brother Dzhokhar, in a white hat, stand near the finish line of the Boston Marathon 10-20 minutes before the first blast. 

Investigators released photographs and video of two suspects and asked for the public's help in identifying them on April 18, three days after the blasts. Later that night, Massachusetts Institute of Technology police officer Sean Collier was shot to death in his cruiser, allegedly by the Tsarnaev brothers. 

Officials secure an area in Watertown, Massachusetts, after the Tsarnaevs had an early-morning gun battle with police. 

Tamerlan was run over by his brother in the shootout and died. Dzhokhar escaped, and around 6 a.m., authorities told residents of Boston and surrounding communities to stay indoors. All mass transit was shut down.

A police officer evacuates a shoeless man holding a child as members of law enforcement conduct a search for Tsarnaev on April 19 in Watertown. 

SWAT teams enter a suburban neighborhood in Watertown. 

A woman carries a girl from their home as a SWAT team searches for Tsarnaev in Watertown. 

An aerial infrared image shows the outline of Dzhokhar Tsarnaev in a boat in the backyard of a home in Watertown.

A telephone call from a resident led police to the boat where Tsarnaev was hiding and a police helicopter detected a heat signal that confirmed his presence there. 

Dzhokhar Tsarnaev, a 19-year-old college student, lifts his shirt while standing in a boat at the time of his capture by law enforcement authorities in Watertown. 

A police officer in Boston reacts to the news that Tsarnaev had been arrested. 

Tsarnaev was sentenced to death on May 15, 2015. The case is likely to go through years of appeals. He is being held at the Supermax prison in Florence, Colorado.

Krystle Campbell, 29, Martin Richard, 8, and Lu Lingzi, 23, were killed in the explosions at the Boston Marathon. 

Sean Collier, 26, an MIT campus police officer, was fatally shot by the Tsarnaev brothers in his patrol car two days after the bombings.