More than 300 murders have gone unsolved in Boston over the last decade, making the city trail behind the national average for unsolved cases, a review of police data by the Boston Herald found.

Of the 628 people murdered in Boston between 2004 and 2013, 336 have yet to be solved, according to the data.

Black males made up the majority of homicide victims during that time, and most killings took place in Roxbury, Mattapan and Dorchester. Guns were the most popular murder weapon used.

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The Herald reports:

The murder clearance rate numbers reported by Boston to the FBI were lower than the average for similar-sized cities for eight of the nine years between 2004 and 2012.

In larger cities comparable to Boston, 62 percent of cases on average were solved, according to the data.

Former Boston police Commissioner Edward F. Davis, who oversaw the department from 2006 to 2013, noted that in Massachusetts, it’s the district attorney’s office — not the police — that acts to charge a suspect, and thus decides when a case is cleared.

That lends itself to a more “conservative environment” compared to other cities where police make the call, Davis said.

“Despite all that, the clearance rate is still low and we fought to improve it while I was there,” Davis said, noting in 2011 Boston police turned to the British model for solving murders, flooding crime scenes with police resources. In each of the following two years, police cleared more than 50 percent of cases — the only two-year success streak for the department during the 10-year period.