Dzhokhar Tsarnaev, who has been charged in connection with the Boston Marathon bombing last week, told investigators that his older brother Tamerlan was the main force behind the attack, with no backing from international terrorist groups, a US government source told CNN.
NPR also confirmed that the initial theory is that the "two young men were working on their own." Law enforcement sources told NPR that the attack was "in a sense a homegrown plot with a little bit of an international flavor" with Tamerlan being the "driving force."
Both CNN and NPR made sure to note that the investigation is still in its early stages, with a lot more evidence left to be uncovered. A federal law enforcement official told CNN "a lot of work remains before they can say confidently that no others were involved."
Only two patients who were wounded in last Monday's bombing, which claimed three lives, remain in critical condition. The Boston Globe reported that the number of people who received treatment for injuries in the wake of the blasts rose sharply to 282 from the initial 170.
Nick Martin, a spokesman for the Boston Public Health Commission said the dramatic rise was due to victims seeking delayed medical attention for injuries or symptoms they expected to go away on their own.
Dzhokhar, 19, has been charged with using and conspiring to use a weapon of mass destruction resulting in death, and malicious destruction of property by means of an explosive device resulting in death.
The court appearance was conducted at Dzhokhar's bedside, with US Magistrate Judge Marianne Bowler finding him "alert, mentally competent and lucid" even though he was heavily sedated and on a ventilator.
Dzhokhar, who was shot in the head, neck, legs and one hand, according to an FBI affidavit, mainly communicated by nodding. He reportedly said, "no" when asked if he could afford representation.
He was initially questioned by federal agents without being read his Miranda rights, under the public safety exception. However, a Justice Department official told CNN that by the time of the proceeding in his hospital room on Monday, Dzhokhar had been read his rights.
The suspect acknowledged his role in placing the explosives on April 15, according to US officials familiar with the interviews cited by The Washington Post. Dzhokhar reportedly told interrogators that America's wars in Iraq and Afghanistan were the motivation behind the attack.
The officials who spoke to The Post also said it appeared that Dzhokhar and his brother were "self-radicalized" and acted without direction from a foreign terrorist organization.
Meanwhile, the FBI is facing scrutiny for failing to register older brother Tamerlan's visit to Russia last year. Sen. Lindsey Graham told Bloomberg that Tamerlan's visit to Russia's Dagestan and Chechnya regions was not noticed by the FBI because an airline misspelled his name.
The FBI reviewed Tamerlan's activities in 2011 at the request of Russia's domestic intelligence service, looking into his family, communications and internet usage.
The issue of the Chechen bombers could be high on the list of priorities when US Secretary of State John Kerry meets with Russian Foreign Minister Sergey Lavrov in Brussels on Tuesday, on the sidelines of the NATO summit.
"Both sides seek to mend ties," Anya Schmemann of the Council on Foreign Relations told the Associated Press. "But it remains to be seen if the Boston bombings offer an opportunity for US-Russian cooperation or if it will lead to an overly aggressive Russian response in the North Caucasus that could be worrisome for the United States."