On Sunday, the chairman of the House Homeland Security Committee said the FBI is now investigating whether the suspects, brothers Tamerlan Tsarnaev and Dzhokhar Tsarnaev, received outside training that helped them carry out the attack.
Analysis of the shrapnel-packed pressure-cooker bombs found they were likely triggered by a toy car remote. This design is not popular with al Qaeda, which suggests the suspects did more research or had outside training to make them.
U.S. officials investigating the bombings have told The Associated Press that so far there is no evidence to date of a wider plot, including training, direction or funding for the attacks. But authorities are searching for anyone who may have helped with the bombs' design.
New information has also been released confirming Russian officials recorded phone calls between Tamerlan Tsarnaev and his mother Zubeidat in which they reportedly discussed jihad.
In another, she was recorded talking to someone in southern Russia who is under FBI investigation in an unrelated case, U.S. officials said.
The calls were intercepted by a Russian wiretap in 2011 and raised Russia's concerns. Russian officials told the FBI only that they had concerns that Tamerlan and his mother were religious extremists and gave no additional information. U.S. officials learned of the wiretap within the last week, according to ABC News.
The news has angered some lawmakers who are now demanding answers.
"They talked about jihad," said Sen. Charles Schumer (D-New York). "Why didn't the Russians let us know that much, much earlier? They should have. And we are asking why?"
According to officials, Tamerlan traveled to Russia following the phone calls where they believe he may have become radicalized.
Tamerlan's body remains unclaimed in a Boston morgue.
His younger brother Dzhokhar is being held at Federal Medical Center (FMC) Devens, a federal prison for male inmates requiring specialized or long-term medical or mental health care. ABC News reports the 19-year-old is in a small cell with a steel door.
U.S. officials say Tsarnaev's mother is a person of interest in the case and would likely be detained for questioning if she came to the U.S.
Zubeidat Tsarnaev has denied that she or her sons were involved in terrorism. She has said she believed her sons have been framed by U.S. authorities.
"It's all lies and hypocrisy," she told The Associated Press in Dagestan. "I'm sick and tired of all this nonsense that they make up about me and my children. People know me as a regular person, and I've never been mixed up in any criminal intentions, especially any linked to terrorism."
Amid the scrutiny, Tsarnaeva and Anzor say they have put off the idea of any trip to the U.S. to reclaim their elder son's body or try to visit Dzhokhar in jail. Tsarnaev told the Associated Press that he is "really sick" and his blood pressure had spiked.
Meantime, the last remaining patient in critical condition from the Boston bombings was upgraded to serious condition Sunday. The patient is being treated at Boston Medical Center.
Another victim from Redondo Beach is showing signs of improvement, loved ones say. John Odom was waiting for his daughter, Nicole, at the finish line when one of the bombs blew up, injuring both of his legs. The victim has undergone several surgeries and faces more.
The Associated Press and ABC News contributed to this report.