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 third of seven sequential photos, Elian Gonzalez is held in a closet by Donato Dalrymple, one of the two men who rescued the boy from the ocean, right, as government officials search the home of Lazaro Gonzalez for the young boy, early morning, April 22, 2000, in Miami, Florida. Armed federal agents seized Elian Gonzalez from the home of his Miami relatives before dawn, firing tear gas into an angry crowd as they left the scene with the weeping 6-year-old boy. This photo won the Prize in 2001. (Photo by Alan Diaz/AP Photo)

Men are held by Iraqi national security agents, to be interrogated at a checkpoint, as oil fields burn in Qayara, south of Mosul, Iraq, Saturday, November 5, 2016. Islamic State fighters launch counterattacks in the thin strip of territory Iraqi special forces have recaptured in eastern Mosul, highlighting the challenges ahead as the battle moves into more densely populated neighborhoods where coalition air power must be used more selectively. (Photo by Felipe Dana/AP Photo)

Police officers detain a Navalny supporter during a protest in St. Petersburg, Russia, Tuesday, February 2, 2021. A Moscow court has ordered Russian opposition leader Alexei Navalny to prison for more than 2 1/2 years on charges that he violated the terms of his probation while he was recuperating in Germany from nerve-agent poisoning. Navalny, who is the most prominent critic of President Vladimir Putin, had earlier denounced the proceedings as a vain attempt by the Kremlin to scare millions of Russians into submission. (Photo by Dmitri Lovetsky/AP Photo)

In this aerial view Haitian migrants queue to receive food at a shelter in Ciudad Acuna, Coahuila State, Mexico, on September 23, 2021. At least 50 police vehicles carrying more than a hundred agents are blocking the border crossing at the river that separates the Mexican city of Ciudad Acuña from the United States, AFP reported. (Photo by Pedro Pardo/AFP Photo)

A man dressed up as the devil jumps over babies lying on a mattress in the street during “El Colacho”, the “baby jumping festival” in the village of Castrillo de Murcia, near Burgos on June 18, 2017. Baby jumping (El Colacho) is a traditional Spanish practice dating back to 1620 that takes place annually to celebrate the Catholic feast of Corpus Christi. During the act – known as El Salto del Colacho (the devil's jump) or simply El Colacho – men dressed as the Devil jump over babies born in the last twelve months of the year who lie on mattresses in the street. (Photo by Cesar Manso/AFP Photo)

Arcelia Aguilar, a resident of “Hogar Jardin De Los Abuelitos”, receives a hug from her niece Maria Aguilar through “El muro de los Abrazos” (The Wall of Hugs) which is a wall made from plastic sheets to protect against the coronavirus, in San Salvador, El Salvador on September 1, 2020. (Photo by Jose Cabezas/Reuters)

Mahmoud El Komy, a 26-year-old Egyptian mechatronics engineer, stands beside Cira 3, a remote-controlled robot that runs tests on suspected coronavirus disease (COVID-19) patients, to limit the human exposure to the virus, amid a second wave of infections in Tanta, Egypt, November 18, 2020. (Photo by Mohamed Abd El Ghany/Reuters)