WASHINGTON (Reuters) – The number of untraceable privately-made “ghost guns” recovered at crime scenes surged nearly 1,600 percent between 2017 and 2023, according to the results of a new federal gun trafficking study released on Wednesday.

The study’s results, announced by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), come after President Joe Biden and Attorney General Merrick Garland in April 2021 directed the agency to oversee a new research initiative to better understand how criminals in the United States obtain their guns.

The study found between 2017 and 2023, 92,702 suspected privately made firearms or “ghost guns,” which can be obtained without background checks and do not contain serial numbers, were recovered and reported to law enforcement.

During that same time frame, the number of ghost guns recovered in crimes grew from 1,629 to 27,490, the ATF said. About 1,700 of them have been tied to homicides, while another 4,000 have been linked to a number of other violent crimes.

The recoveries of illicit machine gun conversion devices, which are used to convert semi-automatic weapons into machine guns, also increased 784 percent, from 658 in 2019 to 5,816 in 2023, the ATF found.

The Biden administration has sought to crack down on the rise of unregulated “ghost guns,” in a bid to tackle concerns about gun violence in the United States.

In October, the U.S. Supreme Court heard oral arguments over the legality of a Biden administration-led effort to regulate them, after a lower court found the ATF had exceeded its authority.

The justices signaled a willingness to uphold the rule, and a decision is expected by the end of June.

Steven Dettelbach, the ATF’s director, said on Wednesday that the study’s findings overall support the need for more background checks before firearms are sold.

“The data show that in 60% of trafficking investigations, the end recipient of a trafficking firearm is a convicted felon,” he told reporters at a virtual news conference.