BRIDGEPORT — A former employee at Riverview Gun Sales in East Windsor pleaded guilty Monday in U.S. District Court to violating a federal firearms law.

Krystopher DiBella, 25, of West Suffield pleaded guilty to aiding in the improper filling out of a federal firearms form, according to the U.S. Attorney. Such a form must be completed by people who purchase firearms from federally-licensed firearms dealers.

DiBella worked at Riverview Gun Sales from 2008 to August 2012 and on several occasions, according to the government, transferred firearms to people who failed to respond to certain questions on the mandatory federal form. Riverview was a federally licensed firearms dealer but lost its license in the aftermath of a raid by federal agents on the business in December 2012.

The charge against DiBella is a result of a sale that occurred on March 15, 2010, the government said. DiBella failed to have a purchaser of a firearm, who was a non-immigrant alien, answer a question on the form regarding U.S. citizenship.

DiBella's sentencing is sentencing for Sept. 16. He faces a maximum one year in prison, five years of probation and a $100,000 fine. The government and DiBella's defense attorney have agreed to recommend a sentence of three years of probation.

As part of the agreement, DiBella will not apply for a federal firearms license or be a responsible party for an FFL for the entire probationary term.

Federal agents raided the Riverview Gun Sales shop a few days after the Dec. 14 Sandy Hook Elementary School shooting. The Bushmaster AR-15 that Adam Lanza used to kill 26 people, including 20 first-graders, at the school was purchased at the store by his mother, Nancy Lanza, authorities have said. Officials have acknowledged that the Bushmaster was purchased legally.

The ATF revoked the federal firearms license of owner David LaGuercia six days after the shootings. LaGuercia had 60 days to appeal the license revocation, but did not, ATF spokesman Deb Seifert said.

While the federal investigation did not involve the gun purchase by Nancy Lanza, it started after investigators reviewed the records of that gun sale. Sources have said that during the review investigators uncovered other evidence that led to the revocation of the firearms license.

The gun shop is familiar to law enforcement authorities. Omar Thornton, the gunman in the Hartford Distributors Inc. mass shooting that left eight people dead in 2010, also purchased guns there, records show.

In December, a South Windsor man who had received a suspended prison sentence and two years probation in May on charges of stealing a dozen rifles and shotguns from Riverview Gun Sales tried to steal a sniper rifle from the same store but was caught.