Boxes of shell casings and firearms line the storage shelves in the Boston Police Department’s ballistics lab, a grim testament to the gun violence that each year leaves dozens dead and many more injured.
Now, in a vast undertaking, a police commander and 12 firearms analysts are examining the thousands of pieces of ballistic evidence collected at crime scenes over the years, then trying to match them to their collection of guns confiscated over the past couple of decades.
Their goal? By determining which spent shells have no matching guns, they will be able to know how many guns used in crimes remain on the streets. As of August, the tally stood at 550.
As part of the systematic review, the analysts are also matching shells to other shells and bullets to determine how often firearms are used and to establish previously unknown connections between crimes, even when the gun has not yet been identified.
The unit’s analysis includes ballistics collected since the start of 2016. But Sergeant Detective Catherine Doherty, commander of the firearms analysis unit, who launched the effort, plans to review shells and other evidence gathered in previous years. Only by knowing the true scope of the problem, she said, can police understand what they are up against.
“I don’t think anyone has ever sat there and tried to figure out how many guns [that were used in crimes] are actually on the street,” Doherty said.
A growing number of police departments — including those in Denver, Milwaukee, and Chicago — routinely analyze ballistics evidence using the National Integrated Ballistic Information Network, known as NIBIN, to identify potential offenders and enhance gun-violence investigations.
The Boston effort expands beyond that practice, systematically reviewing ballistics evidence to figure out how many firearms used in crimes have yet to be recovered. Boston police officials and some criminal justice experts believe the department is the first to conduct such a formal count.
It’s a daunting task. But by tracking down and comparing ballistic evidence, police hope to find more connections between shootings and identify guns that are frequently used, particularly in gang-related violence. They would then analyze that information not only to solve shootings, but to prevent them by targeting specific gangs or offenders who might be involved.
“It helps strategically on where to put resources,” Doherty said. “If detectives know that all of this is connected they could focus on a particular group of people or area. The idea is ‘How many times has that gun been used and can we put it to rest?’ ”
The firearms analysts found that 143 of the 426 discharges of guns this year had a confirmed forensic connection to another gun crime, an indication that so-called “hot guns” are being used multiple times.
This figure includes all incidents in which evidence was collected, even if no one was injured.
In their analysis, officers came across one gun that had been used in as many as eight crimes, suggesting that gangs are sharing guns or that shooters are holding on to the same firearm longer.
Crime specialists say that the department’s effort to track such guns, while far from easy, is likely to pay dividends.
“We’re finding more and more that in a restrictive state like Massachusetts, it’s harder to come by guns,” said Jack McDevitt, a Northeastern University criminologist. “Guns are being shared by gangs or groups of youth . . . that’s huge intelligence. You can start to put a case together.”
But critics say the benefits don’t justify the effort.
“It gives a rough idea of the dimension of the problem,” said Lawrence Kobilinsky, a professor at John Jay College of Criminal Justice in New York and a forensic scientist. “So what? It doesn’t change how police function in solving a crime.”
“There’s probably 10 times more guns out there” than police can quantify, Kobilinsky said.
Boston Police Commissioner William B. Evans said he wants to improve the department’s intelligence about the number of unsolved shootings and believes the database of guns used in a crime can provide crucial information.
“Instead of thinking that it’s a bunch of guns, it’s one gun,” Evans said. “If we can catch the person with that gun, it makes a difference. A simple shell casing can give us the information we need.”
When Doherty was put in charge of the unit in 2014, it had a lengthy backlog of cases, suffered from poor workflow, and was not accredited, Doherty said.
In response, Doherty clarified staff roles to expedite the team’s work, reducing the backlog from some 200 cases to a few dozen. The unit gained its accreditation in February.
Doherty, who has worked for the Police Department for 31 years, grew up wanting to join the “family business,” following in the footsteps of her father, grandfather, and a host of other relatives.
“We do a specific, almost mechanical job where we’re looking at three-dimensional evidence,” Doherty said.
Doherty oversees firearms examiners and ballistic software technicians who spend their days in a lab at the department’s Tremont Street headquarters, analyzing the markings on shell casings, bullets, and firearms.
They take microscopic images of the ballistic evidence using a 3-D computerized machine; evidence is then entered into the National Integrated Ballistic Information Network and scanned for potential matches to guns, other bullets, or cartridge cases.
“It’s like a fingerprint,” said Gary J. Lewis, a firearms analysis officer who retired from the department in May. “These markings are unique to each firearm.”
Probable matches are then visually confirmed in the “scope room.” Examiners spend hours studying a bullet or a shell casing under a microscope, searching for connections between cases and comparing case information, such as locations and suspect descriptions.
As the NIBIN database expands, the likelihood of matches increases.
“The images taken 20 years, 10 years ago, five years ago are all housed in a network,” Doherty said. “What used to take a firearm examiner many years now can be looked at in a 24-hour period.”
There is no shortage of evidence. From the start of 2016 through August, there were 720 shooting incidents in which casings were recovered, Doherty said. Through the first eight months of this year, police had recovered 124 guns that had been used in such cases, compared to 248 last year.
Most common is the 9mm handgun, Doherty said.
In the lab are several buckets of shell casings, collected from across the city. Doherty hopes they can one day be fashioned into a memorial for the victims of gun violence, including Kim Odom, whose 13-year-old son was shot and killed in Dorchester a decade ago.
The families of victims sometimes visit the lab, and Doherty feels obliged to honor their losses.
“They’re so emotional about this place, which is such a cold, barren office, and they were emotional seeing the process here,” Doherty said. “It made me feel that it’s all the more important that we do this job right.”Follow Jan Ransom on Twitter @Jan_Ransom.