A team of American investigators planned to speak with the parents of the two Boston Marathon bombing suspects in southern Russia.
One line of inquiry involves how the brothers may have turned into militants and whether they may have learned their tactics online.
According the Associated Press, the brothers' parents are from Dagestan, a predominantly Muslim province in Russia's Caucasus, where Islamic militants have waged an insurgency against Russia. A U.S. Embassy official said Wednesday that a team of U.S. investigators has traveled to Dagestan to speak to the parents.
Family said that the older Tsarnaev had been influenced by a Muslim convert to follow a strict type of Islam. Tamerlan Tsarnaev, 26, was killed in a shootout with police last week. Brother Dzhokhar Tsarnaev, 19, remained hospitalized after days of questioning over his role in the attacks.
On Sunday, their parents insisted that Tamerlan went to Dagestan and Chechnya last year to visit relatives and had nothing to do with the militants operating in the volatile part of Russia.
Indeed, investigators believe the brothers actually received jihadist training on the Internet, and jihadist websites might have stoked their radical views and given them a recipe for explosive devices.
One counterterrorism expert says the Internet has a growing role in jihad training. Jarret Brachman, director of a security and training center at North Dakota State University in Fargo, N.D., is the author of "Global Jihadism: Theory and Practice," a book published in 2008.
"These kinds of sites allowed [aspiring terrorists] to become complete producers of, not just consumers of, al-Qaida's global mission," he wrote in the Guardian last year.
"Thanks to the Internet, anyone can become a legend. But for some, even legendary status online is not satisfying. Only the taste of blood in the real world is enough."