The older of the two brothers behind the deadly 2013 Boston Marathon bombing had passed a test to become a US citizen three months before the attack, the Boston Globe has reported, citing federal documents.
Tamerlan Tsarnaev, a 26-year-old ethnic Chechen who had immigrated to the United States from Russia a decade before the attack, had correctly answered questions about American history and demonstrated proficiency in English.
But the US immigration officer who reviewed his test did not immediately approve Tsarnaev's citizenship application, the newspaper reported on Monday.
Its report was based on 651 pages of heavy redacted documents released by the Department of Homeland Security.
Tsarnaev was the older of the two brothers who carried out the April 15, 2013, attack, which killed three people and injured 264.
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Three days later he shot dead a university police officer while the pair attempted to flee the city.
He died following a gunfight with police in the suburb of Watertown, Massachusetts, after this younger brother, Dzhokhar, ran him over in a hijacked sport-utility vehicle.
Dzhokhar Tsarnaev, now 22, was found guilty last year of carrying out the attack and sentenced to death. He is a naturalised US citizen.
The files also contained details on Ibragim Todashev, who was shot dead by law enforcement officers during an interrogation in Florida a month after the attack.
The files showed no signs that federal investigators had regarded Tsarnaev or Todashev as security threats prior to the attack, the Globe reported.
