FILE - In this Jan. 28, 2013, file photo, firearms training unit Detective Barbara J. Mattson, of the Connecticut State Police, holds up a Bushmaster AR-15 rifle, the same make and model of gun used by Adam Lanza in the Sandy Hook School shooting, for a demonstration during a hearing of a legislative subcommittee reviewing gun laws, at the Legislative Office Building in Hartford, Conn. Mass shooters have sometimes obtained guns by exploiting limited weapons laws and blind spots in the background-check process or weapons purchased by others. Lanza used his mother's weapons in the massacre at Sandy Hook Elementary School. (AP Photo/Jessica Hill, File)
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