Federal prosecutors in the United States have charged the surviving suspect in the Boston Marathon bombings, Dzhokhar Tsarnaev, with "conspiring to use a weapon of mass destruction against persons and property in the US resulting in death".
He will be tried in a federal - not state - court, and this charge carries the death penalty.
Tsarnaev is still in a hospital bed and unable to speak after suffering a throat wound, reportedly the result of a failed suicide attempt at the climax of a dramatic hunt, when he was found hiding under a tarpaulin covering a blood-stained boat in a residential garden.
Tsarnaev, a 19-year-old Chechen college student, is suspected of carrying out the attacks, which killed three and injured over 170, with his 26-year-old brother, Tamerlan.
Police declined to comment on media reports he was communicating with authorities in writing, with Boston Police Commissioner Ed Davis telling CNN: "There have been widely published reports that he is (communicating silently). I wouldn't dispute that, but I don't have any specific information on that myself.
"We're very anxious to talk to him and the investigators will be doing that as soon as possible."
The charges come on the same day as one of Tsarvaev's alleged victims was laid to rest. Mourners lined up outside St Joseph Church in Medford, Massachusetts, for 29-year-old Krystle Campbell's funeral.
The restaurant manager was one of three people killed a week ago near the race's finish line, where she had gone to watch a friend finish.
Agents are believed to be questioning Tsarnaev over whether he and his brother had accomplices in the attack. They are apparently also trying to find out if there are any unexploded bombs still to be discovered.
It also emerged that Tsarnaev had discussed the Boston Marathon bombings with friends the day after the attack when he returned to the University of Massachusetts campus to use the gym.
Speaking to CNN, a friend claimed Tsarnaev said: “Yeah man, tragedies can happen anywhere in the world. It’s too bad.”
The friend went on to say that, other than appearing a little tired, Tsarnaev seemed otherwise “fine”.
And further details emerged of Tsarnaev’s condition at the time of his arrest late on Friday evening.
Watertown Police Chief Edward Deveau told ABC News: “At the end they were just making demands of him: ‘show your hands, lift your shirt’. And eventually that’s what he did”.
He added: “He was very slow and lethargic in every move that he made and they could see there was no device on his chest. They kept creeping closer to him and then they felt it safe enough to pull him away from the boat”.
Tsarnaev was rushed to hospital, where he was said to be in a serious condition after suffering severe injuries and major blood loss.
Unconfirmed reports suggested he may have been hit once or twice by police bullets the previous evening during the fire-fight in which his brother was killed.
It has also been reported that, as police closed in he may have attempted to commit suicide. That attempt failed but left him with a severe throat wound that required him to be “intubated and sedated” and left him in a critical condition at a Boston hospital.
Tsarnaev’s condition appeared to be downgraded to ‘critical but stable’, although Boston Mayor Tom Menino publically stated that he may never be able to be vocally interviewed because of his throat injury.
Police confirmed that Tamerlan Tsarnaev is likely to have died after his younger brother drove a stolen SUV at police officers who were in the process of arresting the 26-year-old.
Tamerlan was apparently lying handcuffed on the floor after police pounced on him when he ran out of ammunition. He had reportedly approached officers while firing but left his stash of ammunition in the car the brothers had stolen, leaving him vulnerable to arrest as soon as he ran out of bullets.
As Tamerlan was being handcuffed and arrested, police say his younger brother drove the vehicle at high speed towards the group. The police officers were able to dive out the way of the vehicle, but the older brother was hit by the car and dragged for a short distance.
Doctors confirmed that Tamerlan was suffering multiple gunshot wounds, blast injuries and major trauma to his trunk caused by being run over. Offices think it is likely to be the trauma injuries which killed him.
The developments come as debate rages over how much the FBI knew about the activities of Tamerlan Tsarnaev.
The Russian government contacted the agency in early 2011 requesting further information on him, with the FBI confirming this was apparently “based on information he was follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States to the country's region to join unspecified underground groups”.
The FBI apparently responded by checking databases, and interviewing Tsarnaev and his family but said it "did not find any terrorism activity, domestic or foreign".
In a further development, the boys' father, Anzor Tsarnaev, reportedly told Channel 4 News that Tamerlan had called his mother on Wednesday – two days after the bombing – to tell her the FBI had contacted him and they believed he was behind the deadly attack. Tsarnaev reportedly told her that he responded to the FBI accusation by saying "that's your problem".
Republican representatives were quick to jump on the news that the FBI had previously looked into Tamerlan Tsarnaev’s activities, with the Chairman of the House Subcommittee on Counterterrorism and Intelligence Peter King calling the bombings "the latest in a series of cases like this... where the FBI is given information about someone as being a potential terrorist".
Republican Senator Lindsey Graham added that either the FBI had failed or US laws weren't strict enough.
"The ball was dropped in one of two ways… the FBI missed a lot of things, is one potential answer, or our laws do not allow the FBI to follow up in a sound solid way," Graham told CNN.