Dzhokhar Tsarnaev has been found guilty of carrying out the 2013 bombing at the finish line of the Boston marathon.
The guilty verdict means his trial enters a new phase, in which the Boston jury will be asked to decide whether the 21-year-old should face the death penalty.
Jurors convicted Tsarnaev after listening to a month of emotional testimony from survivors of the attack and watching graphic videos of the moment a pair of homemade explosives ripped through the crowds.
Throughout the trial, US government prosecutors described Tsarnaev and his elder brother Tamerlan as hardened terrorists who wanted to kill civilians "to punish America" for its wars in the Muslim world.
The pair fled the scene of the bombing and three days later they murdered a university police officer. They were finally cornered on a suburban street.
Tamerlan was killed during the confrontation but Tsarnaev escaped and was found the next day hiding in a boat.
Speaking about the attack on the marathon, Aloke Chakravarty, one of the prosecutors, told the trial: "He and his brother killed two young women that day. He killed a little boy. They maimed and permanently disfigured dozens of people.
"That day they felt they were soldiers. They were the Mujahideen and they were bringing their battle to Boston."
The defence did not dispute that Tsarnaev, who was 19 at the time of the attack, was responsible for his part in the bombing and did little to counter the government's version of the facts.
Tsarnaev's lawyers argued instead that Tamerlan, the elder brother, was the mastermind of the plot. They portrayed the younger Tsarnaev as a teenager who was in thrall to his older sibling and followed him into terror.
The defence called only four witnesses during the first phase of the trial and are focused instead on the forthcoming fight to prevent Tsarnaev from being executed.
Both prosecution and defence will call new witnesses and make fresh arguments as they debate whether Tsarnaev should be put to death by lethal injection or sentenced instead to a life in prison.
Ultimately, the decision will be in the hands of the jury, who must vote unanimously in order to impose a death sentence.
Families of the victims were in the court as the verdict was read out, including the parents of Martin Richard, an eight-year-old boy who was the youngest of the three people killed in the bombing.
His father, Bill Richard, testified during the trial and described how he had to leave his dying son's side to tend to the wounds of his grievously injured daughter, Jane. The little girl survived the attack but lost her leg.
"I saw a little boy who had his body severely damaged by an explosion and I just knew from what I saw that there was no chance," Mr Richard told the jurors in early March.
"I knew in my head that I needed to act quickly or we might not only lose Martin but we might also lose Jane, too." (© Daily Telegraph, London)
To his father, he was a 'true angel', and to a family friend 'a beautiful boy in a tux' at a prom party. His schoolmates found nothing remotely strange or off-putting about Dzhokhar Tsarnaev.
He was an all-star member of the wrestling team at the prestigious the Rindge and Latin state school in Cambridge, and winner of a $2,500 (£1,676) scholarship in 2011, his final year.
He then won a place at the University of Massachusetts at Dartmouth where his father, Anzor, said he was in the second year of a medical degree.
Dzhokhar Tsarnaev obtained a green card allowing him to stay in the US in 2007, and became a naturalised United States citizen on September 11, 2012.
Friends and acquaintances expressed confusion and dismay at how a sociable if reserved 19-year-old became America's most wanted man, a bomber on the run who spread carnage.
The only outward clue perhaps of Tsarnaev's descent into terrorism was the fact that he was sacked as a lifeguard at Harvard University swimming pool last summer after turning up late once too often. Otherwise, he appeared normal.
But in the privacy of his own home, Tsarnaev had an alternative life, clearly attached to a homeland, Chechnya, he had never even visited, and to its faith, Islam.
On his account with the Russian social networking site, VKontakte (In Contact) he listed his "World View" as Islam and his "Personal Priority" as "career and money". He also had links to pages calling for independence for Chechnya, which lost its bid for secession from Russia after two bloody wars in the 1990s
Friends and acquaintances had no inkling of the real Dzokhar, whom they called Jahar because they were unable to pronounce his name. One classmate vented his shock on Instagram in 2013: "I don't believe I know that bomber…And I've known him for yeaaaarssss!!!! Dzho this is ridiculous man .. what happened bro, I thought u loved us dude!!!!"