"We certainly have ways in national security investigations to find out exactly what was said in that conversation," he told CNN's Erin Burnett on Monday, adding that "all of that stuff is being captured as we speak whether we know it or like it or not."
"It's not necessarily something that the FBI is going to want to present in court, but it may help lead the investigation and/or lead to questioning of her," he said.
More questions arise when it comes to what legal obligation Russell might have had to inform authorities of her husband's identity once the photos went public.
Russell didn't have any legal requirement to call authorities on learning her husband was potentially involved, criminal defense attorney Mark Geragos told Burnett. Spouses can't be compelled to testify against each other in criminal cases.
"Maybe from a moral standpoint she would have wanted to do that," he said.
CNN legal analyst Paul Callan said he didn't believe Russell would be able to enjoy "spousal privilege" against investigators' questions.
"The wife of a criminal defendant generally gets a spousal privilege" if there is a discussion that happened within the context of the marriage, Callan said. "It's protected. That's what spousal privilege is about. But when the husband dies, and where he has revealed what he has told his wife to a criminal co-conspirator, the communication is no longer confidential and the wife cannot claim spousal privilege protection."
The privilege is "really only meant to protect confidential communications to protect the institution of marriage," he said.
Russell can still assert the Fifth Amendment to protect herself, unless she gets immunity from prosecutors, he said.
Defense attorneys often seek immunity for their clients in exchange for providing authorities with information.
"Her lawyer is probably sitting down with her, very worried about the fact that she may face charges herself, depending on the knowledge of the plot," Callan said. "She has to have good information to get a deal from the feds, and that's what we don't know about at this point -- what kind of information to trade."
Russell's day-to-day life
In the meantime, Russell remains largely out of view inside her parents' North Kingstown home, a fleet of unmarked law enforcement vehicles outside whenever she is there.
The federal presence has caused such a disruption the local police have stepped up patrols in the neighborhood out of concern for the Russell family.
She emerges about once a day, often wearing a leopard-print hijab, to travel to her attorney's office in Providence, where she meets with lawyers and federal investigators. The nature of those meetings remains unclear.
While she has not spoken with the public, her attorneys have said Russell is distraught over the loss of life and injuries suffered by bombing victims.
"She cries a lot," DeLuca said last week.