Boston Bombing Suspect's Widow Under Investigation

BOSTON -- The widow of one of the Boston Marathon bombing suspects is under active investigation and could face potential criminal charges related to the deadly blast, law enforcement officials told ABC News.

A spokesperson for the U.S. attorney's office and the FBI declined to comment and authorities said no decision has been made on whether to eventually bring charges while prosecutors concentrate on the trial of Dzhokhar Tsarnaev, Russell's brother-in-law.

Katherine Russell, who was married to Tamerlan Tsarnaev, is suspected of being the woman who accompanied Tsarnaev to a Macy's in Boston two months before the April 2013 attack where the couple bought five pressure cookers - two of which were allegedly used to make the bombs placed at the marathon finish line. In an affidavit to search the Tsarnaev's home, FBI agents said they were looking for clothing consistent with those seen on a security video at Macy's.

A few weeks earlier Tamerlan Tsarnaev had gone to a fireworks store in New Hampshire and bought 48 mortar shells, also used in the bombs. At the fireworks store, Tamerlan had asked for the "biggest and loudest" fireworks available and spent roughly $200, according to court documents.

"To live in a small apartment and buy five pressure cookers and have all those explosives obviously just does not make sense - something other than cooking was going on," said former FBI special agent and ABC News consultant Brad Garrett.

Both lawyers for Russell and federal prosecutors declined to answer ABC News questions about Russell's status, but a senior law enforcement official said she could face charges of misprision of a felony, or failing to notify authorities of a crime about to happen.

Tamerlan Tsarnaev was killed in a police shootout three days after prosecutors say he and his younger brother, Dzhokhar Tsarnaev, detonated twin bombs near the finish line of the Boston Marathon, killing three people - including an eight-year-old boy - and injuring some 260 others.

Days after Tamerlan Tsarnaev was identified as one of the suspected bombers, Russell's attorney, released a statement saying Russell was assisting the investigation into the bombing and was not aware of the plot beforehand.

"As a mother, a sister, a daughter, a wife, Katie deeply mourns the pain and loss to innocent victims, students, law enforcement officers, families and our community," the attorney, Miriam Weizenbaum, said then.

Shortly after the bombing, Russell left her family and moved to New Jersey to live with Tsarnaev's two sisters. She later moved out of her sister-in-law's apartment and was last seen in a transitional housing facility for the homeless in New Jersey, according to authorities briefed on the investigation. Authorities told ABC News the FBI put Russell under surveillance during last year's Boston Marathon race.

Opening statements in the murder trial of Dzhokhar Tsarnaev are set to begin Wednesday morning. Russell is not expected to be called as a witness for the government.