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)

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)

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)

In this September 16, 2017 photo, a music fan poses for the photo against an angel wings' mural at the Rock in Rio music festival in Rio de Janeiro, Brazil. (Photo by Leo Correa/AP Photo)

Alison Brie and Betty Gilpin host in the Netflix comedy-drama“Glow” Season 1 TV Series, 2017. (Photo by Erica Parise/Netflix/Kobal/Rex Features/Shutterstock)

A barn painted with the U.S. flag is seen in the snow covered field in Kanawha, Iowa, United States, January 16, 2016. Iowa will be the first state to hold its primary, with both Democratic and Republican events being held February 1, 2016. (Photo by Jim Young/Reuters)

Jenifer Lopez, 12, watches television at her home in Havana January 9, 2015. (Photo by Alexandre Meneghini/Reuters)