Here is a look at the Boston Marathon terror attack. On April 15, 2013, double bombings near the finish line of the Boston Marathon killed three people and injured at least 264.
Facts: 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.
Victims: 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.
Timeline: 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, describes the bombings as an act of terrorism.
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.
Purported miscommunication 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, an 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 the suspects they are seeking in connection with the bombings. The suspects are later identified as brothers, Tamerlan Tsarnaev, 26, and Dzhokhar Tsarnaev, 19.
Late in the evening, Massachusetts Institute of Technology police officer Sean Collier is shot and killed on campus. Soon after, Tsarnaev brothers carjack a driver in Cambridge. The driver is released about 30 minutes later.
As the police chase them, Tamerlan Tsarnaev and Dzhokhar Tsarnaev throw explosives out the windows and exchange gunfire with officers. Tamerlan 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 Tamerlan Tsarnaev and Dzhokhar Tsarnaev, brothers from Cambridge, Massachusetts. They are of Chechen origin and legally immigrated to the United States. Tamerlan is identified as the person killed in the encounter with police 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 Tsarnaev.
Between 6 and 7 p.m., Watertown resident David Henneberry goes out 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. Law enforcement agents later take Tsarnaev into custody. He is hospitalized in serious condition.
April 22, 2013 - Tsarnaev is charged 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 are initially held on unrelated visa issues. Phillipos, an American citizen, is charged with lying to federal agents.
May 9, 2013 - Tamerlan Tsarnaev is buried in a Muslim cemetery in Doswell, Virginia. This is after cemeteries in Massachusetts and elsewhere refuse to allow his burial.
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 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.
August 13, 2013 - Dias Kadyrbayev and Azamat Tazhayakov plead not guilty to conspiracy to obstruct justice and obstructing justice with intent to impede authorities.
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 confirm that Tamerlan Tsarnaev was accused of participating in a 2011 triple homicide outside Boston.
January 30, 2014 - A notice is filed with a federal court after US Attorney General Eric Holder says that federal prosecutors will seek the death penalty against Dzhokhar Tsarnaev.
May 30, 2014 - Authorities arrest a friend of the Tsarnaev brothers, Khairullozhon Matanov 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. He is also charged with three counts of making materially false, fictitious and fraudulent statements in a federal terrorism investigation. He later pleads guilty to misleading investigators.
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 US 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. Over the course of the trial, prosecutors call 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.
May 15, 2015 - Tsarnaev is sentenced 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 three and a half years in prison for conspiring to obstruct justice and obstructing justice with intent to impede the investigation. Another college friend of 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 admits he is guilty.
July 18, 2015 - Tsarnaev is placed in Supermax prison in Florence, Colorado, also home to inmates Ted Kaczynski, the "Unabomber," and 9/11 co-conspirator Zacarias Moussaoui.
December 22, 2015 - Stephen Silva, the man who loaned Tsarnaev the gun that was later used to kill an MIT officer, is sentenced to time served and three years supervised probation. Silva is also ordered to pay $800 in penalties.
January 15, 2016 - Tsarnaev is ordered to pay more than $101 million in restitution to victims and his request for a new trial is denied.