Two bombs concealed in duffel bags near the finish line of Monday’s Boston Marathon were detonated, spraying shrapnel and debris into crowds of runners and well-wishers. About half of the competitors had already finished the race.

Three were killed, including an eight-year-old boy, and at least 170 injured, some critically. Due to the placement of the explosives, most injuries were to victims’ lower extremities.

Speculation immediately began as to whether this was foreign or domestic terrorism. Some experts noted that the bombs exploded near one another but were spaced seconds apart, a hallmark of extremist groups such as al-Qaida. Others pointed out that the blasts occurred on Patriots’ Day, a civil holiday in Massachusetts commemorating the beginning of the Revolutionary War, as well as the day that federal taxes were due—possible signs of an American, anti-government “lone wolf” perpetrator.

The event is the world’s longest-running annual marathon, with this year’s being the 117th race. It is seen as a soft target since it is open to the public and has few security checkpoints other than in certain private areas. The last comparable attack was the 1996 bombing at the Atlanta Summer Olympics.

The bombs were small but obviously designed to kill and maim, packed with explosives and loose projectiles.

Following the bombing, security was heightened in Washington, D.C., New York City, and Los Angeles, particularly around monuments, landmarks and heavily trafficked areas. Representative Peter King of New York, the chairman of the House Homeland Security Subcommittee on Counterterrorism and Intelligence, told the network, “When you see so many cuts contemplated to Homeland Security and to local police coming from the federal government, this war against terrorism, this was against us, in many ways is more dangerous than prior to 9/11.”

The attack is one more harrowing reminder of U.S. vulnerability to terrorist strikes, regardless of the ideology behind them. For more about what the nation will face in the years ahead, read Real Truth Editor-in-Chief David C. Pack’s free book America and Britain in Prophecy.