The bomb blasts that injured more than 170 people and killed three at the Boston Marathon on Monday continue to rattle the rest of the nation, as Americans mull whether races, ballgames and other sporting events will ever feel safe again.
The twin explosions caused horrific injuries among athletes and fans lining the final stretch of the famous run, but experts say the psychological wounds extend far beyond the 26-mile course.
"The pictures penetrate," said Dr. Arieh Shalev, professor of psychiatry at NYU Langone Medical Center in New York City, referring to images of the bloody aftermath that spread like wildfire on social media. "They bypass all our filters, and we revisit them as we hug our kids and hope this will never happen again."
For Michael Derda, 36, who worked as a medic at the 1996 Olympic Games in Atlanta, the images were all too real.
"They brought it all back," he said, recalling the blast at Centennial Olympic Park that killed two people and wounded 111 more. Running toward the explosion as others fled, Derda helped rescue people who had nails, metal shards and glass embedded in deep, disabling wounds. "It was chaos," he said.
News of the Boston bombings opened old wounds for Derda, who now lives 3,000 miles away in Olympia, Wash. While talking to a counselor and keeping a journal helped ease his anxiety after the Atlanta attack, memories of the deadly blast came racing back Monday.
"It's something that happened and it's never going to go away," he said. "It will always be there."
Experts say it's normal for people to feel anxious, afraid and angry, even if they were miles from the marathon's finish line.
"The greatest fear of all is the fear of the unknown," said Dr. George Everly, associate professor of psychiatry at Johns Hopkins University in Baltimore. "We can cope with just about anything, but we need to know what it is."
Bostonians showed their colors as they rushed to help the wounded Monday, and Everly expects to see that resiliency rise in the weeks to come as information about the attack comes to light.
"Right now is a really tough time because people don't really know what happened. We got over the initial hump but now we're in this trough of ambiguity," he said. "The worst thing we can possibly do is change our way of life. What we don't do is stop going to sporting events."
Across the country, city centers and stadiums are on high alert for suspicious activity and packages.
"We'll all be apprehensive until we find out a little bit more about who did this and why," said Everly. "And we should reassure people that it's O.K. to have certain fears. It's normal. You'd be totally irrational if you didn't."
But for people like Derda, forced back in time by the marathon bombings, those fears come with baggage.
"This will trigger bad memories, and naturally so," said NYU's Shalev, who was chief psychiatrist at Hadassah University Hospital in Jerusalem during two waves of terrorist attacks. "For some people, each additional terrorist attack made them feel worse -- they lost their sleep and whatever gains they had achieved in therapy."
Derda admits his experience in Atlanta made him "jumpy," and he's never been the same.
"People are going to be scared, there's no hiding that," he said. "But when something like this happens, our nation comes together and helps protect and helps heal. The people of Boston are not alone."