The bombs exploded 12 seconds apart near the marathon's finish line on Boylston Street.
According to Richard DesLauriers, the special agent in charge of the FBI's Boston office, the bombs contained BB-like pellets and nails.
The bombs were contained in pressure cookers, hidden inside backpacks, according to the FBI.
Martin Richard, 8, a student at Neighborhood House Charter School in Boston.
Krystle Campbell, 29, of Medford, Massachusetts.
Lingzi Lu, a graduate student at Boston University. She was originally from China.
April 15, 2013 - At approximately 2:50 p.m., two bombs explode near the finish line of the Boston Marathon. The bombs explode within 8-12 seconds of each other, about 50-100 yards apart.
At 6:10 p.m., President Barack Obama speaks to reporters at the White House, "We will find out who did this. We'll find out why they did this. Any responsible individuals, any responsible groups, will feel the full weight of justice."
April 16, 2013 - President Obama, speaking at the White House at 11:30 a.m., describes the bombings as an act of terrorism.
Frederic Wittman, chairman of the board of trustees of the Neighborhood House Charter School in Boston, confirms that one of the people killed is 8-year-old Martin Richard. Richard's sister and mother are hospitalized with serious injuries.
Michael McGlynn, mayor of Medford, Massachusetts confirms that one of the people killed in the attack is 29-year-old Krystle Campbell.
Boston University and the Chinese consulate in New York confirm that the third victim is a female graduate student from China. At the request of her parents, her name is not released at that time.
Officials confirm that there were only two bombs, despite earlier reports that other unexploded devices had been found.
Authorities including bomb experts search an apartment in Revere, Massachusetts, and remove items. Officials caution that there are no clear suspects and the motive remains unknown.
April 17, 2013 - A federal law enforcement official tells CNN that the lid to a pressure cooker thought to have been used in the bombings has been found on a rooftop at the scene.
The name of the third victim is released by Boston University: Lingzi Lu, a graduate student studying math and statistics.
Purported miscommunications between government officials lead several news organizations, including CNN, to report prematurely that a suspect has been arrested and is in custody.
April 18, 2013 - Attorney Kenneth Feinberg, considered the world's foremost expert on victim compensation, is announced as the administrator of The One Fund Boston, a fund to assist individuals affected by the attacks.
At a press conference, the FBI releases pictures of two males they are seeking in connection with the bombings.
Late in the evening, Massachusetts Institute of Technology police officer Sean Collier is shot and killed on campus by the bombers. Soon after, the bombers hijack a car in Cambridge. The driver is released about 30 minutes later.
As the police chase the bombers, the car's occupants throw explosives out the windows and exchange gunfire with officers. One of the bombers is apprehended, but authorities say the other retrieves a vehicle and runs over him as police attempt to handcuff him. The bomber is wounded and later dies at Beth Israel Hospital. He had bullet wounds and injuries from an explosion, according to officials.
April 19, 2013 - Boston police identify the bombers as 26-year-old Tamerlan Tsarnaev and 19-year-old Dzhokhar Tsarnaev, brothers from Cambridge, Massachusetts. They are of Chechen origin and legally immigrated to the United States at different times. Tamerlan Tsarnaev has been identified as the person killed in the encounter with police earlier in the morning, while Dzhokhar Tsarnaev, a student at the University of Massachusetts-Dartmouth, remains at large.
Throughout the day, hundreds of law enforcement officers go door-to-door on 20 streets in Watertown, looking for Dzhokhar Tsarnaev, who authorities believe is still in Massachusetts. Boston-area residents are asked by authorities to stay inside as the hunt continues for the Dzhokhar Tsarnaev.
Between 6 and 7 p.m., Watertown resident David Henneberry goes out for air and to inspect his boat soon after the lockdown is lifted, and sees, "a man covered with blood under a tarp."
8:15 p.m. - Authorities announce they have a person they believe to be Dzhokhar Tsarnaev cornered on a boat in a yard in Watertown, Massachusetts. At some point, law enforcement agents are able to seize the Dzhokhar Tsarnaev. He is transported to a local hospital in serious condition.
April 22, 2013 - Tsarnaev is charged by the U.S. government with one count of using and conspiring to use a weapon of mass destruction resulting in death and one count of malicious destruction of property by means of an explosive device resulting in death.
May 1, 2013 - Three 19-year-olds are arrested in connection with the bombings. The three men are accused of helping Dzhokhar Tsarnaev after the bombing. Federal prosecutors say Azamat Tazhayakov, Dias Kadyrbayev, and Robel Phillipos took items from Tsarnaev's dorm room after the bombing to throw investigators off their friend's trail. Tazhayakov and Kadyrbayev are foreign nationals charged with obstruction of justice, they were both initially held on unrelated visa issues. Phillipos is an American citizen and is charged with lying to federal agents.
May 2, 2013 - The body of Tamerlan Tsarnaev is claimed, and is picked up by a funeral home, according to Terrel Harris, spokesman for the Massachusetts Office of the Chief Medical Examiner.
May 6, 2013 - Robel Phillipos is released into his mother's custody on $100,000 bail.
May 22, 2013 - An FBI agent shoots and kills Ibragim Todashev in Orlando, Florida, while questioning him about his relationship with Tamerlan Tsarnaev after cell phone records connect the two. Todashev tells the agent that Tsarnaev participated in a 2011 gruesome triple homicide that was drug-related. The confrontation between the FBI agent and Todashev turns violent after Todashev lunges at the agent with a weapon, according to a law enforcement source.
July 10, 2013 - Dzhokhar Tsarnaev pleads not guilty to 30 federal charges related to the April attacks.
August 19, 2013 - The testimony of the trauma surgeon who treated Dzhokhar Tsarnaev is unsealed, revealing the extent of his wounds, including multiple gun shot wounds that pierced the base of his skull, mouth and vertebrae. Unsealed documents also reveal that Tsarnaev was not read his Miranda rights until three days after he was detained.
September 13, 2013 - Robel Phillipos pleads not guilty to making false statements to federal officials, and Dias Kadyrbayev and Azamat Tazhayakov reenter their not guilty pleas. Tamerlan Tsarnaev's in-laws appear before a federal grand jury in Boston. Details of the four-hour session are not immediately released.
October 21, 2013 - In a court document, prosecutors in the Boston Marathon bombing case publicly confirm that Tamerlan Tsarnaev was accused of participating in a gruesome 2011 triple homicide outside Boston.
January 30, 2014 - A notice is filed with a federal court after U.S. Attorney General Eric Holder says that federal prosecutors will seek the death penalty against Dzhokhar Tsarnaev.
May 30, 2014 - Authorities arrest Khairullozhon Matanov of Quincy, Massachusetts, and charge him with "one count of destroying, altering, and falsifying records, documents, and tangible objects in a federal investigation, specifically information on his computer, and three counts of making materially false, fictitious, and fraudulent statements in a federal terrorism investigation." Matanov was a friend of the Tsarnaev brothers and ate dinner with them after the bombing.
August 21, 2014 - Dias Kadyrbayev pleads guilty to obstructing justice. As part of the plea agreement, a sentence of seven years will be recommended by the U.S. attorney, and Kadyrbayev, a Kazakh national, has agreed to be deported after serving his sentence.
October 28, 2014 - Robel Phillipos, a friend of Dzhokhar Tsarnaev, is convicted on two counts of lying to federal agents.
January 5, 2015 - Tsarnaev's trial begins.
March 3, 2015 - Jury selection is completed.
March 4, 2015 - Opening statements begin in Tsarnaev's case. Testimony lasts 15 days. The United States calls 92 witnesses; the defense calls four.
April 8, 2015 - After deliberating 11 and a half hours, the jury returns a guilty verdict on all 30 charges. The trial will next move into a penalty phase, where the jury will hear testimony and arguments from both sides and ultimately be tasked with deciding whether he gets the death penalty.
May 15, 2015 - After more than 14 hours of deliberation, the jury sentences Boston Marathon bomber Dzhokhar Tsarnaev to death.
June 2, 2015 - Dias Kadyrbayev, a friend of Dzhokhar Tsarnaev who pleaded guilty in August 2014, is sentenced to 72 months in prison for obstructing justice.
June 5, 2015 - Azamat Tazhayakov is sentenced to 3.5 years in prison for conspiring to obstruct justice and obstructing justice with intent to impede the bombing investigation. Another college friend of Dzhokhar Tsarnaev, Robel Phillipos, is sentenced to three years in prison for making false statements to law enforcement in a terrorism investigation.
June 24, 2015 - Tsarnaev is formally sentenced to death. Addressing the court, he apologizes and says he is guilty.