An unknown number of guns are being built with the mechanisms, causing problems for the police and ATF officials. Photo: An ATF agent holds a generic unfinished receiver, back, and one that has been manufactured, front, at an ATF field office in Washington, on May 06, 2014. The ATF is trying to crack down on the trade in the makeshift guns by targeting shops and individuals who offer to turn the unfinished receivers into functional pieces for firearms. (Photo by Bill O'Leary/The Washington Post)

In this January 27, 2014 photo, snow rollers dot a lot at the northwest corner of Olive and North Main streets in Akron, Ohio. The snow balls are formed naturally when high winds push snow across a hill. (Photo by Michael Chritton/AP Photo/Akron Beacon Journal)

This image released by Esquire shows actress Penelope Cruz on the November 2014 cover of “Esquire” magazine. The magazine has named Cruz The Sexiest Woman Alive for 2014. (Photo by AP Photo/Esquire)

West Berliners crowd in front of the Berlin Wall as they watch East German border guards demolish a section of the wall on November 11, 1989. (Photo by Gerard Malie/AFP Photo)

The Dora the Explorer balloon moves through Times Square during the Macy's Thanksgiving Day parade Thursday, November 23, 2006 in New York. (Photo by Frank Franklin II/AP Photo)

A mural depicting Prime Minister Scott Morrison wearing an unbuttoned Hawaiian shirt, orange lei and Santa Claus hat while holding a cocktail by artist Scott Marsh is seen on a wall in Sydney, Wednesday, December 25, 2019. Morrison was under pressure since taking a much criticized family vacation to Hawaii during the wildfire crisis.(Photo by Steven Saphore/AAP Images via AP Photo)

A bride and groom jump over a skipping rope as they pose during a wedding photo shoot at a park in Pyongyang on April 18, 2019. (Photo by Ed Jones/AFP Photo)

In this Wednesday, April 12, 2017, photo, waitresses wait outside a restaurant in Pyongyang, North Korea. A generational divide is quietly growing in North Korea, often hidden behind relentless propaganda. On the streets there are young women in not-quite mini-skirts and teenage boys with baseball hats cocked sideways, K-pop style. (Photo by Wong Maye-E/AP Photo)