The Russell family hired DeLuca on Saturday, after federal agents contacted them asking to interview her, he said. For now, he is the one speaking to the FBI.
"She understands the need for doing it," he said. "This is the way the government looks at it, and she understands this. It's a threat to national security, and she gets that. And she's a really good person, very sympathetic to that. Katie's just trying to bring up her daughter."
In the statement released Tuesday, DeLuca said Russell is very close to her family.
"She is fortunate to have the support of her loving family now, as they, too, struggle to come to terms with these events and the deep sorrow we all feel following the events of last week," he said. "The injuries and loss of life -- to people who came to celebrate a race and a holiday -- has caused profound distress and sorrow to Katie and her family."
The family released its own statement Friday, after learning Tsarnaev had died.
"Our daughter has lost her husband today, the father of her child," the family said. "We cannot begin to comprehend how this horrible tragedy occurred. In the aftermath of the Patriots' Day horror, we know that we never really knew Tamerlan Tsarnaev. Our hearts are sickened by the knowledge of the horror he has inflicted. Please respect our family's privacy in this difficult time."