US investigators have found traces of female DNA on one of the bombs used in the Boston marathon attacks. But that may not necessarily point to an accomplice.
The DNA could be of a female shop assistant.
But investigators have also begun talking to Katherine Russell, the widow of Tamerlan Tsarnaev.
Younger brother Dzhokhar Tsarnaev is in prison and according to the US media his defense lawyers are negotiating a deal that saves him from death penalty in return for complete disclosure. Parents of the Tsarnaev brothers have alleged their sons were innocent and that they were framed. They are in Dagestan, Russia, and have said they are planning to go to the US.
Meanwhile, the elder brother’s radical links are being scrutinised, here in the US and in Russia.
The two countries are collaborating on the investigations.
Russian authorities have said they have evidence that Tamerlan was in touch with the radical Islamists.
Internet exchanges between them suggested that he was planning to join them.