In the wake of two terrifying and deadly explosions at the finish line of the Boston Marathon on Monday, police identified the Tsarnaev brothers as their main suspects by analyzing countless photos and hours upon hours of video footage from the scene. One video showed one of the brothers dropping a backpack at the site of one of the bombings, and another showed the brothers walking slowly away from the blasts while those around them fled in fear. Then Thursday, the FBI released photos and video to the public, and urged anyone with any information to help out.

"It's likely that the breakthroughs in the case were made by sharp-eyed investigators," said Bloomberg Businessweek's Drake Bennett. But he also offers another possibility: that law enforcement tapped NGI — Next Generation Identification — a huge FBI biometrics program that will eventually be able to cross-reference crime-scene photos and video with a massive database of 12 million images.

In recent years, the FBI has invested roughly a billion dollars in developing NGI, with the hopes that it will dramatically speed up identification work, allowing the feds to automatically scour huge amounts of digital evidence in just seconds — it really is meant to find that proverbial needle in a haystack. The technology, some of which is still in development, includes iris scanning, voice recognition, and facial scanning software, and some funds will go toward increasing the number of closed-circuit security cameras (which Boston already has, and may have played a role in identifying the Tsarnaevs). 

Law enforcement officials are now loading mugshots into a massive network, which they'll soon be able to compare with photos from crime scenes. NGI won't be fully operational until next year, but pilot plans are running in a few states, and technology is developing. Earlier this week, California tech company AOptix released a hand-held biometrics tool that police and border patrol officers can plug into their iPhones.

One can see how, even in its relative infancy, NGI and related digital tools may have really helped police this week. 

Of course, NGI remains controversial — civil liberties advocates fear such a database allows the government to monitor innocents. Senator Al Franken spoke at a hearing about NGI last July, stating, "You can change your password. You can get a new credit card. But you can't change your fingerprint, and you can't change your face. Unless, I guess, you go to a great, you know, deal of trouble."