Katherine Russell Tsarnaev still faces charges after Boston Marathon bombings

Katherine Russell Tsarnaev, the widow of Boston bomber Tamerlan Tsarnaev, still faces the threat of criminal charges and remains “of interest” to Federal and State investigators four months after the terror attack.

Katherine Russell, 24, has met with investigators several times since the bombs were detonated at the finish line of the Boston Marathon on April 15.

A source close to the investigation has told MailOnline that law enforcement officials “still want to know what she knows”, and have not ruled out bringing charges.

The source said: “We are still very interested to know what she knows and can’t rule out anything at the moment in terms of future charges or where the investigation will take us.

“So no we’ve not ruled out bringing charges. This is an ongoing investigation and she’s of interest. We are proceeding carefully and thoroughly. It’s not over.”

Her attorney, Amato DeLuca said: “Katie has co-operated with the government extensively. Hopefully, they will conclude that Katie should not be charged.”

Katherine Russell did not meet with Federal investigators until April 22 – a full seven days after the bombings – when several agents spent just 15 minutes speaking with her lawyers at the Russell family’s Rhode Island home.

In the months since the bombs that killed four and wounded 264, with many suffering horrendous wounds including loss of limbs, Katherine Russell’s behavior and movements have been a source of great interest and scrutiny.

In May, CNN reported one key area of interest is a telephone call made by Katherine Russell to her husband shortly after authorities released his and his brother’s picture to identify them as suspects during the manhunt in the days after the bombings.

The FBI is believed to have retrieved the content of that conversation. Although information collected in this way is rarely presented in court, it can inform the course of investigations and interviews.

In May, Katherine Russell added New York attorney Joshua Dratel to her legal team, a criminal lawyer with experience in defending terrorism cases.

Until then Katherine Russell had been content to be represented by Amato DeLuca, a longtime family friend and a specialist in civil cases such as personal injury law.

Joshua Dratel’s expertise is very different. He has represented terrorism suspects in federal courts and military commissions with Guantanamo Bay detainee, David Hicks, one of his most famous clients.

David Hicks attended an Al Qaeda training camp in Afghanistan. He spent more than five years in Guantanamo and went onto serve a nine-month sentence in Australia having pleaded guilty to terrorism charges in March 2007.

Speaking at the time, Amato DeLuca explained Katherine Russell’s decision and said: “Mr. Dratel’s unique, specialized experience will help insure that Katie can assist in the ongoing investigation in the most constructive way possible.”

The move to bring Joshua Dratel on board came after it was reported by the Washington Post that investigators had discovered radical Islamist files on Katherine Russell’s computer.

It remains unclear whether the extremist files found on Katherine Russell’s home computer belonged to her or were downloaded by her late husband, Tamerlan Tsarnaev or his younger brother Dzhokar, 19, who is currently awaiting trial.

They included content from al-Qaeda magazine Inspire, which has featured articles such as, Make A Bomb in the Kitchen of Your Mom.

Investigators have speculated that this may have provided the blueprint for the homemade bombs – two pressure cookers packed with shrapnel – which were detonated with such devastating effect.

Despite submitting not guilty pleas to 30 charges, including using a weapon of mass destruction to kill, Dzokhar Tsarnaev allegedly told arresting officers that he and his older brother built the pressure cooker bombs in the basement of the Cambridge, Massachusetts, apartment building in which Tamerlan and Katherine Russell lived.