Three days after two bombs exploded near the finish line of the Boston Marathon on April 15, 2013, the FBI was getting desperate. They thought they knew who did it, at least they had video of the two young men who appeared to plant the bombs, but they didn't know who the men where or, more importantly, where they were.

But the Bureau had one card to play: they could release the videos to the public. There were drawbacks to that play.

"We were concerned that if we released the photos, the bombers would know that we were on to them. They might decide the jig was up and that it was time to make a last stand," William Weinreb, the lead prosecutor in the Boston bombing case, told the Combating Terrorism Center at West Point in a recent interview. "On the other hand, you don’t want to go too long without making the pictures public and essentially crowd-sourcing the identification process. The ultimate goal is to determine who they are before they decide to regroup and commit another offense or flee the country or any number of things that would be bad for public safety. It’s always a tough choice that involves balancing many competing concerns."

Amid the internal debate, the FBI knew that news organizations could get hold of the footage and publish at any time, and that fact eventually tipped the scales. At 5:00 p.m. on April 18, the FBI released photos and videos of the suspects and appealed for the public's help in identifying them. Next came the flood.

"After the pictures were published -- within those first 24 hours -- we had 10,000 online tips, 10,000 videos, and 113,000 images that were sent to us," said Harold Shaw, who has served as the Special Agent in Charge of the Federal Bureau of Investigation’s Boston Division since 2015. "How did we handle that within a 24-hour period? We needed to triage it. We have a transfer system where we can intake information and get it down to our headquarters. There, 150 agents and analysts were standing by to exploit and analyze it. What pictures or images were relevant? What’s a real video or still image that was actually taken at the scene?"

Read: Timeline of the Boston Marathon Events (Boston.com)

The deluge of information didn't directly lead to the bombers, Dzhokhar and Tamerlan Tsarnaev. The brothers were caught after carjacking a local man and then getting into a shoot-out with police that claimed Tamerlan's life. But all those photos and videos were critical for putting Dzhokhar away for good.

"You’re not only looking at this information for lead or intelligence purposes, you’re also looking at it for evidentiary purposes," Shaw said. "Did you go through all of it? Is there information that helps you identify a co-conspirator? Is there information that might be exculpatory to individuals who may not have been involved? That was a huge lesson learned from the Boston Marathon bombing. Looking at a picture or a video, it’s really some compelling evidence. Although scouring through digital media can be laborious and challenging on a number of accounts, it can be invaluable evidence and really move a case along."

The sheer breadth of the tips from the public is one of a few interesting details from Weinreb and Shaw's interview with the CTC. Another is that during the hunt for the bombers, Shaw, an FBI agent, was personally briefing Director of the CIA John Brennan -- evidence, he said, of how far the intelligence community has come in cooperation since the Sept. 11, 2001 attacks.

Primary Source: A View From the Foxhole: Five Years After the Boston Marathon Bombing (CTC)

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