“Nothing broken but my heart,” was the subject line on an e-mail from one of the Boston Marathon runners to his friends Monday night after the bombs had detonated near the finish line. And every American shared some of that trauma as a classic sporting ritual was turned into a scene of mayhem.

As the FBI and Boston police gathered evidence Tuesday, a preliminary picture emerged: The two bombs were rudimentary “improvised explosive devices,” or IEDs, left on the ground and detonated by remote control from a cellphone or other electronic device. The bombs were packed with metal objects, such as nails and ball bearings, like the IEDs that have been so deadly in foreign battlefields.

Because the bombs were placed on the ground, they did maximum damage to people’s legs — a cruel irony at the finish line of America’s premier event for distance runners. The bombs were not complicated or made of high-velocity explosives. They were simple and easily replicable.

U.S. intelligence didn’t pick up any threat stream about Boston or the marathon before the event, nor any terrorist “chatter” about the attack afterward. That doesn’t rule out al-Qaeda involvement, but this attack doesn’t resemble anything the core group or its major affiliates have done in the past.

Officials can only speculate at this point about perpetrators. But the early evidence looks more like the work of a lone individual or a small group than that of a larger terror network. If it’s part of a broader terror plot, then it represents a new and cruder approach. Terror attacks that fit the same pattern are the 1995 Oklahoma City bombing, the 1996 pipe bombing at the Atlanta Olympics and the 2011 pipe-bomb plot in Spokane, Wash. In each case, the chief attackers were lone wolves.

Officials are focusing on the basics: They’re analyzing all the surveillance data gathered in the area around Boylston Street, before and after the bombs went off, and all the forensic evidence at the crime scene. The intelligence agencies are listening on every circuit they have overseas and the FBI is doing the same at home.

As on Sept. 11, 2001, the most effective counterterrorism force is the public. Officials argue that the most important lesson is this: If you see something, say something. Public vigilance will be the most effective defense against crude attacks that are easy to organize and hard to detect.

“The Boston attack is another harsh reminder that terrorism can be immediate, intimate and random,” says Hank Crumpton, a former top CIA counterterrorism specialist and the author of “The Art of Intelligence.”

The sophisticated counterterrorism systems the United States have developed since 2001 will be helpful, but only up to a point. Surveillance systems were deployed throughout Boston for the marathon, and especially near the finish line, and every available law-enforcement officer was on duty. But that didn’t stop the bombings. It’s reassuring that all the cameras and other surveillance gear, and the analytic systems to interpret the raw data, will help generate leads. But the Boston bombings show that surveillance technology isn’t a panacea.

The Boston attack also shows the limits of intelligence collection, at home and abroad. Terrorists have become more sophisticated in evading detection. They maintain better discipline in keeping their communications out of monitoring range, as demonstrated by Osama bin Laden’s amazing years of hiding in plain sight in a Pakistani military town. They have learned how to foil surveillance cameras by using light disguises.

“Humint,” the jargon term for gathering intelligence from real human beings, remains the hardest challenge. Seeing into the minds of adversaries was difficult with an organization that numbered into the hundreds, like the core of al-Qaeda. It will be much tougher with small, decentralized groups or individuals.

A decade has taught the United States that the most destabilizing consequence of 9/11 wasn’t the terrorist act itself but the way the country responded. America was knocked off-balance: Costly wars in Iraq and Afghanistan sapped public morale without achieving clear gains. A sort of calm seemed to be returning after the counterterrorism storm — until the Boston attack.

Perhaps the most striking thing Monday was how well the public and local law enforcement reacted to the disaster. Good crisis plans had been prepared, and police and first responders followed them. Individual citizens were calm and courageous and took care of each other. Terrorism is a part of modern life, but it didn’t win any victories Monday in Boston.


Read more from David Ignatius’s archive, follow him on Twitter or subscribe to his updates on Facebook.