Video by Evan Perez, Evelio Contreras and Robert Bikel, CNN Text by Evan Perez, CNN  On a recent night in New Orleans, a relatively quiet period with few shootings was shattered in the 7th Ward.  Two men, 19 and 23 years old, were smoking marijuana in a car. Shots rang out.  A man jumped out of a car, ran up behind the parked vehicle and fired, a few witnesses said.  Police found 15 shell casings.  Blood covered the seats and stained the pavement.  A bullet was found lodged in the frame of the driver-side door, inches from the head of one victim. The two men were rushed to the hospital. One of them had been shot twice before.  Still, this is a case with few leads.  Meredith Acosta, a top analyst for the NOPD crime lab, arrived at the scene to collect the shell casings as technicians photographed and catalogued the scene.  Back at the crime lab, Acosta and her team analyzed the casings.  The murder rate in New Orleans is coming down after years of deadly street violence by drug gangs that outmatched the police department.  One tool making a difference is the federal ballistics database called NIBIN, the National Integrated Ballistic Information Network.  Run by the Bureau of Alcohol, Tobacco, Firearms and Explosives, it's a computer library akin to a finger-print database â but for guns. Shell casings recovered at crime scenes around the country are analyzed and stored in the NIBIN database, which crime lab analysts can use to match to firearms in other crimes. Within minutes crime lab analysts can tell if the gun has been used in other crimes around the city.  In New Orleans, that is a key piece of the crime-solving puzzle. The NOPD estimates there are 600 to 700 gang members in the city. They often share guns, using the same weapon in multiple crimes. Thatâs a major intelligence advantage for police, who can connect crimes and suspects to one another.  There are images for 354,000 bullets and 2 million cartridge cases in the database.  On the wall in Acosta's office is a large diagram with interconnected circles noting case numbers. The diagram shows how suspects and guns are linked to each other.  Like any database, it's only good as the information it holds.  In this case, the gun used in the 7th Ward either hasn't been used in other crimes, or hasn't been catalogued before. No match.  The shell casings recovered in this shooting are now in the database. From experience, police say there is a high likelihood it will be used again.
Every gun has a signature and every bullet tells a story. Meet a team in New Orleans thatâs using data to help lock up criminals.