* Senate panel wants to know how Russia trip was missed
* Official injury toll increased to 264
The wife of the dead Boston Marathon bombing suspect is assisting authorities and she is in absolute shock that her husband and brother-in-law were accused of the deadly blasts, her lawyer said on Tuesday.
The 19-year-old brother-in-law Dzhokhar Tsarnaev, who survived shootouts with police and has been criminally charged, was upgraded to "fair" from "serious" condition on Tuesday at Beth Israel Deaconess Medical Center, the U.S. Attorney's Office in Boston said.
Tamerlan Tsarnaev, 26, was killed in a shootout with police last week as authorities hunted for him and his younger brother. The FBI had identified the brothers as suspects last Thursday, based on pictures and video taken at the scene of the bombing on the marathon finish line on April 15.
A lawyer for Katherine Russell, 24, said she was busy caring for their two-and-a-half-year-old daughter and working as a home healthcare aide in the time leading up the blasts that killed three people and wounded more than 200.
"She is doing everything she can to assist with the investigation," the lawyer, Amato DeLuca, said outside his Providence, Rhode Island office. "The reports of involvement by her husband and brother-in-law came as an absolute shock to them all."
Russell, an American-born convert to Islam, is not a suspect. Officials have identified only the ethnic Chechen brothers Tamerlan and Dzhokhar Tsarnaev as suspects.
Tamerlan died after a shootout with police on Friday, and at a hospital bedside hearing on Monday, Dzhokhar was formally charged with using a weapon of mass destruction and malicious destruction of property resulting in death. The charges could carry the death penalty if he is convicted.
Dzhokhar was recovering from gunshot wounds suffered during at least one of his two gun battles with police. He was captured on Friday night following a massive, daylong manhunt that shut down greater Boston.
Dzhokhar told investigators in his hospital room he and his brother acted alone, without any help, according to reports by NBC, CNN and the New York Times. He said his older brother was the driving force behind the bombings, the reports said. Reuters could not independently confirm the information.
Police say the Tsarnaev brothers also killed a university police officer on Thursday night and wounded a transit police officer on Friday morning.
DeLuca, the widow's lawyer, declined to say what law enforcement agencies Russell had spoken with or what they have asked her. "It is pretty evident that she didn't know anything," DeLuca said.
"She cries a lot," DeLuca said. "She can't go anywhere. She can't work."
A total of 264 people were injured in the blasts, the Boston Public Health Commission said on Tuesday. Hospitals reported 10 people lost limbs from the bombs packed with nails and ball bearings and 48 patients remained hospitalized as of Monday, two of them in critical condition.
The Tsarnaev brothers emigrated to the United States a decade ago from Dagestan, a predominantly Muslim region in Russia's Caucasus. Tamerlan was a legal U.S. resident and Dzhokhar became a U.S. citizen last year.
Russian authorities flagged the older Tsarnaev in 2011 as a possible Islamist radical, and some lawmakers have accused the FBI of failing to act thoroughly enough after Russia's security services raised their concerns. The FBI questioned him in 2011.
At a Senate Judiciary Committee hearing on immigration legislation, Republican Senator Lindsey Graham of South Carolina asked Homeland Security Secretary Janet Napolitano why the older brother was not questioned upon returning from Russia in 2012.
Napolitano said U.S. Customs generated an alert upon him leaving the country but neither Customs nor the Federal Bureau of Investigation was aware of his return six months later.
"The FBI text alert on him at that point was more than a year old and had expired," Napolitano said.
Napolitano also dispelled reports authorities may have lost track of Tamerlan Tsarnaev because his name was spelled differently on an airline manifest.
The elder brother, a legal U.S. resident, visited relatives in the volatile region of Chechnya for two days during his six-month trip out of the United States last year, his mother, Zubeidat Tsarnaeva and aunt, Patimat Suleimanova, told Reuters in Dagestan on Monday.
Proud but angry, Tamerlan Tsarnaev never quite achieved his own idea of the American dream, and instead found solace in a radical form of Islam adopted by fighters in his homeland, according to people interviewed by Reuters.
U.S. authorities were investigating whether he became involved with Chechen separatists or Islamist extremists there.
Top investigators were scheduled to brief the full House of Representatives behind closed doors on Tuesday about the failure to spot the danger, and the full Senate was expected to receive a briefing later in the week.