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)

Soldiers use electronic sensors to search for missing firefighters under a line of fire trucks caught in massive gas explosions in Kaohsiung, Taiwan, Friday, August 1, 2014. A series of underground explosions about midnight Thursday and early Friday ripped through Taiwan's second-largest city, killing scores of people, Taiwan's National Fire Agency said Friday. (Photo by Wally Santana/AP Photo)

A man sleeps at Beirut's Corniche, a seaside promenade, in Lebanon May 2, 2016. (Photo by Alia Haju/Reuters)

A soldier of the Household Cavalry Mounted Regiment falls off a horse during a practice to participate in the state ceremonial surrounding this year's Platinum Jubilee celebrations at Hyde Park in London, Thursday, March 31, 2022. Around 170 horses and personnel of the Household Cavalry Mounted Regiment left their Hyde Park Barracks to form up and be inspected by the General Officer Commanding the Household Division, Major General Christopher Ghika. (Photo by Frank Augstein/AP Photo)

The AMECA robot from the manufacturer Engineered Arts is in the Deutsches Museum Nuremberg (Future Museum), Bavaria on May 3, 2022. AMECA is a humanoid robot that will be presented to the general public for the first time in Europe as part of the Blue Night on May 7, 2022 in Nuremberg. (Photo by Daniel Karmann/dpa/Alamy Live News)

The Wadi al-Salam cemetery, Arabic for “Peace Valley”, is seen in Najaf, south of Baghdad, Iraq August 3, 2016. The world's largest cemetery, in Iraq's Shi'ite holy city of Najaf, is expanding at double its usual rate as Shi'ite militias bury their dead from the war against Islamic State. The Wadi al-Salam cemetery, Arabic for “Peace Valley” has a special place in the hearts of Shi'ite Muslims as it surrounds the Mausoleum of their first imam, Ali Bin Abi Talib, a cousin and son-in-law of Prophet Mohammad. (Photo by Alaa Al-Marjani/Reuters)

A storm whips through a tented area occupied by Nepalese earthquake survivors as a mother grabs her infant child and runs to find shelter in Kathmandu, Nepal 23 May 2015. Nepalese, who lost their homes in earthquake and fear aftershocks, have been living in temporary shelter in open ground which they had to flee because of the heavy rain and powerful wind. (Photo by Narendra Shrestha/EPA)

An employee dressed in a Santa Claus costume plays with cats at the Catgarden in Seoul, South Korea, December 14, 2020. (Photo by Kim Hong-Ji/Reuters)