In response, the FBI interviewed Tamerlan and his family and searched databases, but they did not find any evidence of "terrorism activity, domestic or foreign." During the 2012 trip to Dagestan, Tamerlan was reportedly a frequent visitor at a mosque on Kotrova Street in Makhachkala, believed by the FSB to be linked with radical Islam. Some believe that "they were motivated by their faith, apparently an anti-American, radical version of Islam" acquired in the U.S., while others believe that the turn happened in Dagestan. At the time of the bombing, Dzhokhar Tsarnaev was a student at the University of Massachusetts Dartmouth with a major in marine biology. He became a naturalized U.S. citizen on September 11, 2012. Tamerlan's boxing coach reported to NBC that the young brother was greatly affected by Tamerlan and admired him. Tamerlan was previously connected to the triple homicide in Waltham, Massachusetts, on the evening of September 11, 2011, but he was not a suspect at the time. Brendan Mess, Erik Weissman, and Raphael Teken were murdered in Mess's apartment. All had their throats slit from ear to ear with such great force that they were nearly decapitated. The local district attorney said that it appeared that the killer and the victims knew each other, and that the murders were not random. Tamerlan Tsarnaev had previously described murder victim Brendan Mess as his "best friend." After the bombing and subsequent revelations of Tsarnaev's personal life, the Waltham murders case was reexamined in April 2013 with Tsarnaev as a new suspect. Both ABC and "The New York Times" have reported that there is strong evidence which implicates Tsarnaev in this triple homicide. Some analysts claim that the Tsarnaev's mother Zubeidat Tsarnaeva is a radical extremist and supporter of jihad who influenced her sons' behavior. This prompted the Russian government to warn the U.S. government on two occasions about the family's behavior. Both Tamerlan and his mother were placed on a terrorism watch list about 18 months before the bombing took place. On April 15, several people who were near the scene of the blast were taken into custody and questioned about the bombing, including a Saudi man whom police stopped as he was walking away from the explosion; they detained him when some of his responses made them uncomfortable. Law enforcement searched his residence in a Boston suburb, and the man was found to have no connection to the attack. An unnamed U.S. official said, "he was just at the wrong place at the wrong time."