A George Mason University student described by federal prosecutors as an “active trafficker of firearms” for his alleged sale of homemade pistols with no serial numbers and devices to convert guns into automatic weapons was arraigned this week in federal court in Alexandria.

Davud Sungur, 20, was arrested in March after allegedly selling eight guns to undercover Fairfax County police officers, court records show. Beginning in January, he allegedly sold other weapons to undercover officers, including three 9mm pistols that he had constructed using parts purchased legally online but that didn’t have serial numbers. Police call these unserialized weapons “ghost guns,” which are legal to own but not sell.

Authorities nationwide have expressed concern about guns without serial numbers, which are difficult to trace. D.C. police said the number of ghost guns they have recovered has soared and such weapons have been used in nine homicides since 2017. Ghost guns have also been used in a number of high-profile shootings around the country, including the 2013 killings of five people in Santa Monica, Calif., by a man prohibited from buying a gun. The District last month sued the main manufacturer of homemade gun kits, Polymer80, for violating the city’s consumer protection laws.

According to an affidavit filed before his arrest in March, Sungur told two undercover officers that he also had a 3-D printer at his home in Fairfax City and was able to make a plastic piece known as a “drop in auto sear” to modify a weapon. The auto sear is inserted into the gun near the trigger to make it fire continuously while the trigger is held down, turning a semiautomatic weapon into an automatic one.

In 1981, the Bureau of Alcohol, Tobacco, and Firearms ruled that auto sears constituted a machine gun part and they were declared illegal. Sungur reportedly told the officers this as he sold them an AR-15-style rifle with an auto sear in January and another auto sear with a homemade 9mm pistol in February, according to an affidavit written by Special Agent Gordon Cummings of Homeland Security Investigations.

Sungur was arrested after an alleged fourth sale to police March 18 and ordered held without bond. His attorneys said in a bond motion that he is a full-time student at George Mason with no criminal history.

Federal prosecutors said Sungur told police that he sold guns to customers around the country. In four meetings with the undercover officers, Sungur allegedly sold three homemade pistols, two rifles and eight commercially made handguns for nearly $7,000, according to court records. When police searched his family’s home near the George Mason campus, they found a 3-D printer and a MAC-11 machine pistol, prosecutors said.

In addition, Fairfax police told federal investigators that while they were executing a search warrant in November related to a murder case, they found an AK-47 rifle, though not the murder weapon, Cummings wrote. The original purchaser of the rifle told police that he had sold the rifle to Sungur, which led prosecutors to believe “the defendant sold firearms to a juvenile and continued to deal in weapons for months thereafter,” according to a filing by Assistant U.S. Attorney John C. Blanchard.

In opposing bond for Sungur, prosecutors also said the Virginia crime lab reported shell casings from the November killing were similar to those used by the homemade 9mm guns allegedly sold by Sungur to police in January and February.

U.S. District Judge Liam O’Grady declined to release Sungur on bond.

A federal grand jury indicted Sungur last week on charges of dealing firearms without a license and unlawfully transferring a machine gun, and he was arraigned Wednesday.

One of his attorneys, Peter D. Greenspun, declined to comment on the case Wednesday.