The federal complaint was unsealed Tuesday when William Dong, 23, appeared in federal court in New Haven.
In September, Dong traveled to Pennsylvania, purchased a Bushmaster model XM-15-E2S, .223-caliber semi-automatic rifle and transported it back to Connecticut., according to the statement from Daly.
This firearm is a prohibited assault weapon under Connecticut state law.
On Dec. 3, Dong was arrested by West Haven Police near the University of New Haven campus in West Haven after he was found in possession of two loaded handguns on his person and the loaded Bushmaster rifle, which was seized from his nearby car, the statement said.
A witness noticed the stock of a rifle in Dong's vehicle and called police after seeing him run toward campus, which was placed on lockdown. Dong, a commuter student who lived in Fairfield, was apprehended after walking out of a class, university police said.
Dong told police that he had purchased the rifle from a seller in Pennsylvania in September through an advertisement placed on www.armslist.com, the statement said.
A search of his home on Stratfield Road in Fairfield by police turned up 2,700 rounds of ammunition and a collection of clippings about the deadly 2012 shootings at a theater in Aurora, Colo.
Although it is not unlawful under federal law for an individual to possess this Bushmaster firearm, it is a federal violation for an individual to purchase this firearm outside of Connecticut and travel into the state with it, because it is a prohibited firearm under Connecticut state law, the statement said.
The federal charge carries a maximum penalty of five years in prison and a $250,000 fine.
Dong faces state charges of illegal possession of an assault weapon and breach of peace.
Dong, who has been in state custody since his arrest Dec. 3, appeared Tuesday before U.S. Magistrate Judge Joan G. Margolis in New Haven. He agreed to a federal order of detention and waived his right to a speedy indictment and a probable cause hearing.
The Bureau of Alcohol, Tobacco, Firearms and Explosives is working with the West Haven Police Department to investigate the incident. Assistant U.S. Attorney Robert M. Spector is prosecuting the case.
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