But neither brother appears to have been legally entitled to own or carry firearms where they lived, a fact that may add to the national debate over current gun laws. Last week, the U.S. Senate rejected a bill to expand background checks on gun purchases, legislation that opponents argued would do nothing to stop criminals from buying guns illegally.

Tamerlan Tsarnaev, 26, who was killed in the shootout with police, would have been required to apply for a gun license with the local police department where he lived in Cambridge, Massachusetts.

But there is no record of him having done so, according to Cambridge Police Department spokesman Dan Riviello.

Even if he had earlier received a gun license from somewhere outside Cambridge, that license would have to be registered with Cambridge police upon becoming a resident of the city, Riviello said. In Massachusetts, gun licenses are issued by municipal police departments.