Two more friends of convicted Boston bomber Dzhokhar Tsarnaev were jailed on Friday for impeding the FBI investigation into one of the deadliest attacks on U.S. soil since 9/11.

A U.S. judge sentenced Azamat Tazhayakov, a student from an affluent family in Kazakhstan, to three-and-a-half years for obstruction and conspiracy. 

A knife-wielding man killed by the terror investigators who had him under surveillance was confronted because he had bought knives and talked of an imminent attack on "boys in blue," the FBI said Wednesday.

Usaama Rahim plotted for at least a week to attack police, the FBI said in a complaint against a family member who was arrested Tuesday, the day Rahim was shot to death. On Wednesday, the relative, David Wright, was ordered held on a charge of conspiracy with intent to obstruct a federal investigation.

One man was arrested and a knife-wielding suspect shot dead in Boston in connection with an alleged terror plot targeting law enforcement and military personnel, police said Wednesday.

The U.S. attorney's office identified the suspect in custody as David Wright and said he would appear in a federal court on Wednesday.

A man under surveillance as a possible terror suspect was shot dead by police and the FBI outside a Boston pharmacy Tuesday after brandishing a knife at officers, police said.

Local media identified the man as being in his mid-20s and of Middle Eastern descent, but his name was not revealed. 

A college friend of convicted Boston bomber Dzhokhar Tsarnaev was sentenced to six years in prison Tuesday for obstructing justice in hindering the FBI hunt for the perpetrators of the 2013 attacks.

Dias Kadyrbayev, 21, from Kazakhstan, was one of three friends who went to Tsarnaev's dorm room at the University of Massachusetts, Dartmouth after the FBI released images of him as a suspect.

Boston bomber Dzhokhar Tsarnaev, a 21-year-old naturalized American of Chechen descent, will be formally sentenced to death in court on June 24, a U.S. judge said Thursday.

Judge George O'Toole's sentencing comes after a jury decided unanimously that Tsarnaev should die for his role in the 2013 Boston Marathon attacks that killed three people and wounded 264 others.

Survivors of the Boston Marathon bombings said justice had been served but reacted with mixed emotions after a jury handed down the death penalty verdict to convicted killer Dzhokhar Tsarnaev.

"He's going to go to hell. That's where he wanted to go," said Michael Ward, a firefighter who was off duty at the time of the April 15, 2013 attacks but who treated victims at the scene.

A U.S. jury on Friday sentenced 21-year-old Dzhokhar Tsarnaev to death for his role in the 2013 Boston Marathon bombings, one of the worst assaults on American soil since the September 11, 2001 attacks.

It took the jury more than 14 hours to choose death rather than life imprisonment for the ex pot-smoking college student of Chechen descent, who came to the United States as a child and took citizenship in 2012.

In the moment the Amtrak train that derailed at a curve this week was supposed to be slowing down, it was accelerating, investigators said Thursday.

How that came to happen has emerged as the central question surrounding the derailment, which killed eight people and sent more than 200 to hospitals Tuesday night in the deadliest U.S. train wreck in nearly six years.

A jury began a second day of deliberations Thursday on whether to sentence Boston bomber Dzhokhar Tsarnaev to death or life imprisonment, for perpetrating one of the worst attacks in America since September 11.

The 12 men and women, who last month convicted the 21-year-old of Chechen descent on all charges relating to the April 15, 2013 bombings, must reach a unanimous verdict if they are to sentence him to death.