It was not clear how long the public safety exemption could be used. Attorney General Eric Holder wrote in a 2010 memo the FBI believed "that in light of the magnitude and complexity of the threat often posed by terrorist organizations, particularly international terrorist organizations, and the nature of their attacks, the circumstances surrounding an arrest of an operational terrorist may warrant significantly more extensive public safety interrogation than would be permissible in an ordinary criminal case."
The brothers were immigrants to the U.S. from the Russian Caucasus, an area that includes Chechnya and Dagestan. Tsarnaev was born in Kyrgystan, came to the United States in 2002, and became a citizen on September 11, 2012. His older brother was not a U.S. citizen but was in the country legally.