I took this photo at the finish line of the Boston Marathon. Everywhere you looked, people were taking photos with phones, point-and-shoots and DSLRs.

When I was snapping photos at the finish line for the Boston Marathon, I had no idea that there could be bombs at my feet. 

It was my last day in Boston after a long weekend and I was three hours away from getting on a plane to head back to San Francisco. I decided to check out the event after hearing my Bostonian friends and family rave about the Patriot Day activities.

I used my iPhone to snap a few photos of my Boston observations: a gorgeous church at the finish line, a little girl on her mother’s shoulders as she took photos with mommy’s smartphone, and finally, a wide panorama shot from my spot at the race’s final stretch.

The first two photos went to my Instagram feed, but the last panorama didn’t resonate with me. It was a sloppy shot, with weird stitching and unclean borders. I had taken it in haste right before heading back on the subway. I even considered deleting it, but I didn’t. And two days later, I was sending it to the FBI. 

What I didn’t know about that panoramic photo at the time was I was capturing it just a few yards from the site of the second bomb that exploded near the finish line of the Boston Marathon on Monday. I didn’t know that I could possibly be taking photos of the person who dropped off a hacked pressure cooker bomb that was set to go off at 2:50 p.m. — just one hour and 20 minutes after I took the photo. I also had no idea that I could be taking photos of people that could end up being among the 3 dead and more than 170 injured from the bombings, nor that I was risking being one of them myself.

I learned of the bombings after I got to the airport. I had already gone through security when my friends started texting and calling me — frantic after seeing my recent Instagram photo from the finish line. I spent the remaining time before my flight staring at one of the many CNN-blaring television sets in Logan airport, praying that TSA would do an extra security check before I boarded my flight to LAX. (They didn’t, by the way.) 

After six and a half long, news-free hours, I landed in California, spending my 30-minute layover calling and texting the people who had left me messages while I was in the air.

This photo was taken just past the finish line at the Boston Marathon.

It wasn’t until Tuesday that it occurred to me that I had taken a photo that could be helpful to the FBI investigation. I skimmed a few articles about how the FBI was collecting photos and video as evidence and could not find an easy email to send my photos to. Instead, I dropped a “tip” on the FBI website, telling them to email me if they wanted my photo.

The next morning, I got an email from a counter terrorism agent based in San Francisco. I sent him my photo and shortly after, I received a call from him. He asked me a few questions about where I took the photo in relation to the blast. At the time, I wasn’t sure. I was gone by the time the bombs exploded and I hadn’t watched near enough cable news to memorize the blast maps. (I now know that the blast was to the left of me.) 

After explaining that I wasn’t there when the bomb when off, the agent’s questions turned to whether I had seen anything suspicious. I hadn’t. In fact, I was having a lovely morning. The atmosphere was buzzing with joy and celebration as the elite runners made it to the finish line. There was nothing to indicate the carnage that was about to take place. That was part of what made it so shocking.

The agent wanted all of the photos I had taken that day and I gladly sent him them, including that panorama I had almost deleted. (The FBI is still asking for Boston Marathon spectators to submit their photos to assist in the investigation -- if you have photos taken at the scene, you can send them to boston@ic.fbi.gov.)

My panoramic photo from the finish line of the Boston Marathon Monday, taken a little over an hour before two bombs exploded nearby.

I was very hesitant to share this photo with the public. While I was quick to use it to help with the investigation, I wasn’t sure that I wanted to publish it. It is by far the creepiest photo that I’ve ever taken. Looking into the faces of the people watching the marathon, you see unsuspecting victims. (Not to mention the fact that the stitching in the iOS panoramic feature made it look like some runners didn’t have legs -- especially spooky considering the gruesome effect the bombs would have when they exploded at ankle-height.)

While it’s not surprising that civilian photos are being used in an FBI investigation, the potential amount of raw footage under review may be unprecedented. The general public has collectively captured the event in high resolution and can send the data instantly to the authorities. The ubiquitous camera phone and the popularity of the social networks we use to share our photographs has us all recording and broadcasting more than ever before. The advent of new life logging devices and wearable tech like Google Glass is sure to increase this even further. And though we often question and consider what these advances mean for photography and our society in terms of personal privacy, recent events also highlight their potential role in public security.

Lauren Crabbe, @lcrabbe, is a freelance technology writer and photographer, specializing in photography technology and trends. You can find her biking around San Francisco, drinking a lot of coffee and capturing her daily observations with her iPhone on whatever app she is testing that day.