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)

Christ the Redeemer is seen from the Vista Chinesa (Chinese View) during sunrise in Rio de Janeiro, Brazil, May 4, 2016. Rio de Janeiro is a marvel and a mess all at once. When it hosts the first ever Olympics in South America, starting Aug. 5, visitors will see a city whose stunning topography – stark, verdant mountains loom over packed and playful beaches – competes only with the drama of daily life here. (Photo by Ricardo Moraes/Reuters)

A Palestinian female masked militant from the Al-Quds Brigades, the military wing of the Islamic Jihad, takes part in an Islamic Jihad rally in Rafah, southern Gaza Strip, 29 July 2016. (Photo by Mohammed Saber/EPA)

In this November 28, 1966 file photo, one of the 10 beagles involved in the first test of the Veterans Administration Hospital in East Orange, N.J. smokes a cigarette through a machine linked to its windpipe by a plastic tube to test any link between smoking and emphysema. (Photo by AP Photo)

This 2014 series Shanghai Tian Wa saw Chinese photographer Liu Tao train his lens on two distinct districts in Shanghai. Here: “Shanghai Tian Wai №26, 2014”. (Photo by Liu Tao/The Guardian)

A goat hops from student to student during a goat yoga class at the University of Tennessee on August 25, 2022 as part of welcome back week. The session was organised by Goat Yoga Nashville. (Photo by Matt Hamilton/Chattanooga Times Free Press via AP Photo)

An Afghan girl rides a horse at the beach in Karachi, Pakistan, 07 September 2020. (Photo by Rehan Khan/EPA/EFE)

A girl wearing a face mask as a precaution against the coronavirus walks past a display of garments at a market in Bengaluru, India, Saturday, January 9, 2021. India will kick off the coronavirus vaccination drive on Jan. 16 to stem the pandemic in the world's second-most populous country. A Health Ministry statement says that priority will be given to the healthcare workers and the frontline workers, estimated around 30 million. (Photo by Aijaz Rahi/AP Photo)