U.S. President Barack Obama on Friday night lauded the law enforcement efforts in detaining a suspect of the Boston bombing, while noting that many questions remain to be answered.

Obama made the televised statement from the White House briefing room shortly after authorities took 19-year-old Dzhokar Tsarnaev in custody following a day-long manhunt.

Despite the detainment, the president said, "there are still many unanswered questions," such as what motivated the bombers and who helped them.

"Why did young men who grew up and studied here as part of our communities and our country resort to such violence? How did they plan and carry out these attacks?" Obama added.

The president also mourned the victims in Monday's bombings and the following police operation, and praised the law enforcement and local residents in greater Boston area.

The American people, he stressed, refused to be terrorized by such a "heinous act."