The official, who is not authorized to comment publicly, said the source of the DNA is "unknown,'' adding that it could belong to any one of a number of people, from the point of the bomb-component's manufacture and distribution to sale.

Authorities had taken a sample of DNA from Tsarnaev's widow, Katherine Russell, earlier in the week as investigators sought to learn more about the suspected bomber's activities during the time leading to the April 15 attacks and the days immediately following.
The explosions near the finish line of the famed race killed three people and injured more than 260.
On Thursday, a law enforcement official said investigators are seeking Russell's cooperation in learning more about Tsarnaev's activities and communications leading up to the attacks.
Investigators have been specifically interested in a telephone call Tsarnaev made to her on April 18, three days after the bombings, after the FBI first circulated photographs of Tsarnaev and his 19-year-old brother, Dzhokhar Tsarnaev, as suspects. The content of the phone conversation between the two has not been disclosed.
Ọmọ Oódua, News From Nigeria,  USA Today