Riverview Gun Sales of East Windsor, Conn., which also allegedly sold a weapon used in another Connecticut mass shooting, had its federal firearms license, listed under the name of shop owner David LaGuercia, revoked six days after the Newtown shooting, and LaGuercia's 60-day appeal period has expired, the Bureau of Alcohol, Tobacco, Firearms and Explosives said.
LaGuercia had no immediate comment.
The shop remains open, selling ammunition, gun accessories such as targets and hearing protection, and clothing.
ATF agents raided the shop for undisclosed reasons shortly after the Dec. 14 school shooting and before it pulled LaGuercia's license Dec. 20, the Hartford (Conn.) Courant reported.
WFSB-TV, Hartford, reported a man with mental illness was seen on video surveillance walking out of Riverview Gun Sales with an AR-15 semi-automatic rifle.
Nancy Lanza legally purchased an AR-15 that was alleged to be among the guns her son Adam Lanza used to kill 26 people, including 20 first-graders, at Sandy Hook Elementary School, the Courant said.
The federal investigation didn't involve Nancy Lanza's gun purchase but started after investigators reviewed the records of that gun sale, the Courant said, citing sources who said the review uncovered other evidence that led to the license revocation.
U.S. Attorney's Office spokesman Tom Carson told United Press International Friday he couldn't "confirm or deny that there is a criminal investigation" related to Riverview.
LaGuercia said in December he was "absolutely appalled" to learn a gun he sold to Nancy Lanza might have been used in the Newtown massacre.
"There is nothing more devastating than the loss of a child and I am absolutely appalled that the product that was sold several years ago would be used in this type of crime," he said in the statement cited by The Journal News of White Plains, N.Y.
"Our hearts go out to the victims' families and, as a father of three, I know firsthand of a parent's loss and it's the worst nightmare," his statement said, adding he was "cooperating with law enforcement in their efforts to get to the bottom of this senseless tragedy."
LaGuercia's shop, which describes itself on its website as "one of Connecticut's largest gun dealers," allegedly also legally sold two Ruger SR9 semi-automatic pistols used in an Aug. 3, 2010, shooting at a Hartford Distributors Inc. beer-distribution warehouse in Manchester, Conn., that left nine people dead including the gunman, former employee Omar Shariff Thornton.