The officials, who spoke on condition of anonymity to describe an ongoing investigation, said Dzhokhar and his older brother, Tamerlan Tsarnaev, who was killed by police as the two attempted to avoid capture, do not appear to have been directed by a foreign terrorist organization.
Rather, the officials said, the evidence so far suggests they were “self-radicalized” through Internet sites and U.S. actions in the Muslim world. Dzhokhar Tsarnaev has specifically cited the U.S. war in Iraq, which ended in December 2011 with the removal of the last American forces, and the war in Afghanistan, where President Obama plans to end combat operations by the end of 2014.
Obama has made repairing U.S. relations with the Islamic world a foreign policy priority, even as he has expanded drone operations in Pakistan and other countries, which has inflamed Muslim public opinion.
Dzhokhar Tsarnaev has provided limited information to authorities that indicates he and his brother acted independently, without direction or significant influence from Islamist militants overseas. U.S. officials said they are still working to assemble a detailed timeline of a trip the older Tsarnaev took to Russia, but see no evidence that he received instructions there that led to the attack.
“These are persons operating inside the United States without a nexus” to an overseas group, a U.S. intelligence official said.
U.S. officials have said that the FBI questioned Tamerlan Tsarnaev at the behest of Russian authorities who had become concerned that he was becoming radicalized. The request was conveyed to officials at the U.S. Embassy in Moscow. U.S. officials said they sought follow-up information from Russia, but that Moscow failed to respond.
Officials also expressed skepticism that Russian authorities were concerned about the elder Tsarnaev’s contacts during his trip to Russia. “The evidence points to the fact that they let him into the country and let him out of the country,” the U.S. official said. “They didn’t take any legal action, which they could have while he was there.”
The Boston Public Health Commission said Tuesday that at least 250 people have sought medical treatment at area hospitals for injuries related to the bombings. The number has gradually increased in the past week as people seek delayed help for minor injuries that didn’t heal on their own or hearing problems, according to a spokeswoman for the health commission.