For former New York City Mayor Rudolph Giuliani, Monday's explosions at the Boston Marathon were a gruesome reminder that terrorism can strike at any time.
"This is the world we've been living in since Sept. 11," Giuliani said during an interview Monday on "The Michael Kay Show" on ESPN 98.7 FM. "We've been remarkably fortunate in not having too many of these attacks. A lot of that goes to the great work done by the police and the CIA and the FBI and our military."
"These people are relentless. Though, if this is a terrorist attack, I don't know if it's an Islamic extremist terrorist attack, or some kind of other terrorist group," he said. It hasn't been determined whether the attack was an act of international terrorism. "We have to assume the worst, at least the police and law enforcement have to assume the worst, there will be other attacks, and they have to protect people based on their plan they have for dealing with priority targets."
The two bombs that detonated near the marathon's finish line on Boylston Street in Boston killed three people and have injured upwards of 100.
Giuliani, who served as New York City's mayor during the Sept. 11, 2001 terrorist attacks, remembers going through safety protocols for outdoor events, like the Boston Marathon, and trying to ensure safety in a public place.
Giuliani said New York dealt with terrorist threats on New Year's Eve while he was mayor, and he nearly canceled the Times Square event in 2000. Even with all the focus on security for large outdoor events, there's always the possibility that something can go wrong.
"You do the best that you can. You deploy hundreds if not thousands of police officers," Giuliani said. "When New Year's Eve happens, the police actually for three of four days go underground, opening the manhole covers, making sure there are no bombs there. Checking people, being very, very careful about who's let in. You do everything you can do, but human beings are human. You can do everything you can do, then one person, two, three people can slip through and then you have a horrible thing like this."
Giuliani said the protocol in New York City for an attack like Monday's would be to send police to places that he described as "priority attack list" points. Those are areas that might be attack points based on information police have gathered from arresting and questioning terrorists. In Boston, he said the focus is on securing other parts of the city and ensuring safety of targeted area.
"Half of this response by the Boston law enforcement will be to protect the rest of Boston, half of it will be to deal with the incident and save as many people as possible," Giuliani said. "But you have to bifurcate here, you have to focus on the incident itself and then you have to worry about if this is a signal that there will be other attacks."
Giuliani acknowledged that there is no way to know when the time is right to resume normal activity, such as the playing of sporting events. Monday's Boston-Ottawa NHL game in Boston was postponed and Tuesday's Celtics-Pacers game was canceled.
"You just go on instinct. Sometimes you're right, sometimes you're wrong," Giuliani said. "The victory parade in '01 we thought would be OK because we were already beginning to come out of it. Baseball had already taken four to five days off and Broadway closed for four or five days.
"I remember going on 'Saturday Night Live' and telling people when they came back on the air, it's OK to laugh now. You have to try as sensitively as you can to get people back to normal. You can't just remain in a constant state of focusing on the event and being immobilized."
He added: "Obviously we have to be cautious but we can't stop doing the things we do. Otherwise these terrorists win, or whoever is doing this wins, by immobilizing us."
In 2001, Giuliani served as the face of New York, leading the city back in its revival. He's confident that Boston and all those affected will recover.
"This is the threat we live with," Giuliani said. "[I grew up] with the threat of nuclear war with Soviets, and our grandparents and parents lived through the threat of Nazism and the great war in which we lost many, many more people than we've lost so far in this era of terrorism.
"I would urge people: Don't feel too sorry for us. Our parents and great grandparents went through things just as bad as this, I think actually worse. If they can get through it, we're strong enough to get through this."