The two suspects in the bombings of the Boston Marathon had “international ties” and “military experience,” NBC News reported on Friday.

The suspects are brothers with the last name Tsarnaez and are from the Russian republic of Chechnya, law enforcement sources told the broadcaster.

NBC reported that the brothers, aged 19 and 20, have permanent resident status in the United States, where they have been living for about a year.

Boston police and federal authorities are conducting a massive door-to-door manhunt for the 19-year-old, NBC said, after the 20-year-old was killed in a shootout with police early on Friday.

The official said the older brother died in a shootout with police and the younger one was being sought in a house-to-house search for in the Boston suburb of Watertown.

The brothers had been in the United States for several years, the official said. National security and law enforcement officials said they were leaning toward the theory that the bombings were motivated by Islamist extremism.

A U.S. law enforcement official and the uncle of the suspects in the Boston Marathon bombings are confirming that the name of the second suspect is Tamerlan Tsarnaev, the older brother of Dzhokhar A. Tsarnaev, 19. Tamerlan Tsarnaev was killed in a gun battle with police in Massachusetts on Thursday night.

Three law enforcement officials, speaking on condition of anonymity due to the sensitivity of the ongoing investigation, confirmed the bomb suspects were brothers. One of the officials and the men’s uncle confirmed the identity of Tamerlan Tsarnaev.

The uncle, Ruslan Tsarni of Montgomery Village, Maryland, told The Associated Press that the men lived together near Boston and have been in the United States for about a decade. They traveled here together from the Russian region near Chechnya.

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