The two native Chechens authorities believe bombed the Boston Marathon had become radicalized Muslims and were motivated by U.S. military involvement in Iraq and Afghanistan, according to several reports.

The two were acting as jihadists, motivated by Muslim religious anger at the U.S., the surviving brother told interrogators, reports the Wall Street Journal.

Tamerlan Tsarnaev was killed last week in a shootout with police. His 19-year-old brother and alleged accomplice, Dzhokhar, remains hospitalized with multiple bullet wounds.

Tamerlan apparently sent text messages to his family in Russia in 2011 suggesting he was willing to die for Islam, reports Fox News. During initial questioning, Dzhokhar told the FBI he had only recently been recruited by his brother in the attack that killed three and wounded more than 180 at the marathon's finish line.

The Boston bombing took place days after a deadly attack in Afghanistan killed 17 civilians, including 12 children. The Afghan government has blamed the CIA for the attack, reports the New York Times.