Investigators have found traces of female DNA on a fragment from one of the bombs that exploded at the Boston Marathon earlier this month, U.S. officials said late Monday.

While it is still unclear who the DNA matches to, the find indicates a female accomplice may have helped the two brothers suspected in the bombings, Tamerlan and Dzhokhar Tsarnaev, according to officials briefed on the probe speaking to U.S. press.

Investigators will now compare the DNA of Katherine Russell, the widow of accused bomber Tamerlan, against the DNA found on the bomb remnant to determine if she ever came in contact with the device, U.S.-based CBS news reported on Tuesday.
Russell is not a suspect in the bombings.

“FBI agents met with Russell at her parents' Rhode Island home Monday to collect a DNA sample,” the CBS report stated.

Tamerlan died after a shootout with police four days after the April 15 bombings.

"The FBI is there as part of our ongoing investigation, but we aren't permitted to discuss specific aspects of the case," FBI spokesman Jason Pack was widely quoted as saying by the U.S. press.
Boston bombing suspects Tamerlan Tsarnaev (L) and Dzhokhar Tsarnaev. (Al Arabiya)

Russell has remained silent, staying with her three-year-old daughter Zahara at her parents’ house in Rhode Island. Russell's family has issued a statement saying they were shocked by the attack.
Still, investigators want to question Russell to find out if she had any knowledge of her husband's plans.

In 2009, Tamerlan was arrested for assaulting Russell.
Still, investigators want to question Russell to find out if she had any knowledge of her husband's plans.

Her school friends have reportedly said she was “brain-washed by her extremist husband.”

Meanwhile, the Tsarnaevs' parents have denied their sons were involved in terrorism.
The father of the bombing suspects has accused the FBI of “setting up” his sons.

“They just wanted to set up Tamerlan, and Dzhokhar just turned out to be in the wrong place at the wrong time,” Anzor Tsarnaev told the Russian Komsomolskaya Pravda daily last week.
“Tamerlan was driving him to school when they started shooting at them,” he said. “This is a set-up, a political order, a Hollywood show.”

Zubeidat Tsarnaeva, the suspects’ mother, has also said she believed her sons have been framed by U.S. authorities