WASHINGTON — The FBI has found female DNA on at least one of the two homemade bombs detonated during the Boston Marathon on April 15, according to a law enforcement official.

The presence of genetic material does not necessarily mean a woman helped build the pressure-cooker bombs, said the official, who spoke on condition of anonymity because the investigation is ongoing.

The genetic material could have come from a woman who was in the room where the devices were built or from a cashier at a store where one of the bomb parts was purchased, the official said.

The test results have prompted investigators to look more closely at women who may have had contact with the alleged bombers, Tamerlan Tsarnaev and his younger brother, Dzhokhar Tsarnaev.

Investigators are collecting DNA samples from some women who were close to the pair to provide a comparison. Reuters said investigators removed bags of evidence including some containing DNA samples from the home in Rhode Island where Katherine Russell, the widow of Tamerlan Tsarnaev, has been living.

Meanwhile, prominent death penalty lawyer Judy Clarke is joining the team representing Dzhokhar Tsarnaev. Her clients have included Unabomber Ted Kaczynski; Susan Smith, who drowned her two children; and most recently Tucson, Ariz., shooter Jared Loughner. All received life sentences.