Such data, in the rare instances it has been publicly released, has illuminated the pathways through which legally manufactured and lawfully sold firearms are obtained by criminals.
Jason J. Eaton, 48, of Burlington, was charged with shooting three college students of Palestinian descent on Saturday outside the building where the police said he lives.
The site was built for the military, but commercial sales are booming with little public accountability. Rounds have been bought by murderers, antigovernment groups and others.