While the explosions left hundreds visibly hurt, the event may have also left thousands with invisible scars.
Just a few days ago, Laura O'Flaherty finished her second Boston Marathon race, but the sights, the sounds and the emotions of this year's race haven't necessarily left her with happy memories.
“You're there hugging someone because you're excited of the jubilation of the marathon, and then you're hugging someone because you're consoling them,” said O’Flaherty. “So that kind of mind shift kind of puts you in panic mode and makes you pretty somber about a situation like that.”
She finished about 30 minutes before the explosions happened.
Nancy McCoy of Tomah finished just 15 minutes before.
“I turned around and talked to a marathoner that had finished four minutes before the bombs went off, and he started tearing up when we started talking,” said McCoy.
“It's going to create impacts, it's going to create memories, it's going to create visions,” said therapist Todd Hoffe.
Hoffe said traumatic events like the explosions at the Boston Marathon can lead to symptoms of Ppost-traumatic stress disorder, or PTSD, including depression and anxiety.
“If it's ongoing, it can affect the major areas of your life,” said Hoffe.
But PTSD could affect more than just the hundreds of runners and thousands of spectators at the event.
With things including the Internet, Facebook and Twitter, graphic images and videos of the event can be seen anywhere over and over again.
“It definitely has an effect,” said Hoffe. “In this age, it happens fast, and then of course you can dig deeper when you're on the computer and it has a little click on where you can go to more images or more stories or more witness events. That can be kind of consuming with you.”
He said for some runners, these images will stay with them for the rest of their lives. Others may get better with time, and everyone copes in their own way.
"I requalified for the marathon,” said McCoy. “I wasn't going to, but I feel like I should.”
Hoffe said it’s important for people to look into professional help if they are having trouble dealing with what happened and talking about it with family and friends doesn't seem to be working.
If left untreated, the symptoms of PTSD can become life-threatening.