For four days, America languished in uncertainty about whether the Boston Marathon bombing was the work of an al-Qaida terrorist cell or some other foreign operation.

On Friday, the country awoke to the knowledge that the prime suspects were two young brothers, immigrants from the Caucasus region, who lived for 10 years in Cambridge, Mass., home of two of America's most prominent universities, Harvard and the Massachusetts Institute of Technology.

By day's end, one suspect was dead and the other, still in his teens, was in custody following a massive manhunt that had the entire Boston region in lockdown for much of the day. Police finally brought the man into custody at 8:45 p.m. EST.

Locals responded to news of the arrest with jubilation, then joined the rest of the nation in asking why. What would compel two young men to take part in such a heinous crime and, as police say, be so committed to continue their killing spree?

<NO1><NO><NO1><NO>Police identified the suspects as Dzhokhar and Tamerlan Tsarnaev, brothers who came from a region of Russia near Chechnya about 10 years ago. Tamerlan Tsarnaev, 26, the man in a black baseball cap identified by the FBI as Suspect No. 1, was killed during a confrontation with police earlier in the day. The younger brother, Dzhokhar Tsarnaev, 19, was later arrested behind a residence in Watertown, Mass.

The hunt for those responsible for the bombing at the Boston Marathon accelerated after the FBI released photos and video of two suspects on Thursday and asked for the public's help in identifying them. It culminated in a confrontation and shoot-out that left an MIT police officer dead and a transit police officer seriously wounded.

</CS>While the identification of the suspects and the arrest Friday provide some sense of relief, these developments leave a trail of new questions. Were these brothers working for a larger terrorist network, perhaps one connected to Chechnya, which has been torn apart by an Islamic insurgency and has been the scene of numerous deadly bombings? Or were they part of a larger, equally troubling narrative, of young American men engaging in massive violent attacks? America has already witnessed too many of these cases in locations such as Aurora, Colo.; Newtown, Conn.; Oakland and many other locations just in the past year alone.

These scenarios appear both possible as well as unlikely. A Chechen terrorist attack in the United States would be a first. Although there are indications that the older brother may have been converted by radicalized Islamists, the boys' uncle strongly rebutted the possibility of any connection between the youths and the troubles in Chechnya. Meanwhile, friends described the younger brother as friendly, sociable and involved in school activities.

"I never would have suspected this," a former school friend of Dzhokhar Tsarnaev told a Boston-area TV station. "You just don't expect these (suspects) to be from Cambridge."

There was a time when we wouldn't expect these things in America at all. At least, with one suspect in custody, the nation may get some answers to questions left behind.