A Syrian man rides his bicycle past a man selling grains during a halt in fighting on February 29, 2016 in Douma, in the Eastern Ghouta region, east of the capital Damascus. A UN-backed ceasefire deal took hold across parts of Syria, bringing relative calm to areas where the Islamic State group and Al-Qaeda's local affiliate are not present. (Photo by Sameer Al-Doumy/AFP Photo)

Participants in traditional dress ride on horseback as they enjoy the atmosphere at the Feria de Abril (April's Fair) on April 12, 2016 in Seville, Spain. The Feria de Abril has a history that dates back to 1857 and takes place a fortnight after Easter each year. The origin of the fair was a cattle market but the event quickly turned its goal from commerce to having fun. More than 1 million local and international participants are expected to attend the Feria de Abril. (Photo by David Ramos/Getty Images)

Girls sleep in the back of their father's moto-taxi as he watches them from the front seat, days after an earthquake in Pedernales, Ecuador, Wednesday, April 20, 2016. A fresh tremor rattled Ecuador before dawn Wednesday, a magnitude-6.1 jolt that set babies crying and shaken residents pouring once again into the streets, fearful of yet more damage following a monster earthquake over the weekend. (Photo by Dolores Ochoa/AP Photo)

Pedestrians and workers pass an upside down car art installation in a car park on the South Bank in London, February 19, 2015. British artist Alex Chinneck's illusory piece, entitled “Pick yourself up and pull yourself together”, and on display in the working car park for a week, sees a Vauxhall car suspended upside down, appearing to be gripping onto a peeled back length of tarmac. (Photo by Toby Melville/Reuters)

A general view of the residential area is pictured during dusk at Jodhpur in Rajasthan, April 5, 2015. Jodhpur, also known as the blue city in the desert Indian state of Rajasthan, which residents say originally, was used to show where the highest caste of priestly Hindus live, who wanted to set them apart from the rest of the population. Later the rest of the population followed suit. Another reason for the city to be blue is to keep the buildings cool during the summers, local residents said. (Photo by Adnan Abidi/Reuters)

The Ivanpah Solar Electric Generating System is seen in an aerial view on February 20, 2014 in the Mojave Desert in California near Primm, Nevada. The largest solar thermal power-tower system in the world, owned by NRG Energy, Google and BrightSource Energy, opened last week in the Ivanpah Dry Lake and uses 347,000 computer-controlled mirrors to focus sunlight onto boilers on top of three 459-foot towers, where water is heated to produce steam to power turbines providing power to more than 140,000 California homes. (Photo by Ethan Miller/Getty Images)

A nurse helps an injured bomb victim sitting at the back of a pickup truck at the Asokoro General Hospital in Abuja, April 14, 2014. A morning rush-hour bomb killed at least 35 people at a Nigerian bus station near the capital on Monday, raising concerns about the spread of an Islamist insurgency after the first such attack on Abuja for two years. Suspicion fell on Boko Haram, though there was no immediate claim of responsibility from the Islamist group mainly active in the northeast. Five hours after the blast, officials had given no death toll. Reuters journalists counted at least 35 bodies. (Photo by Afolabi Sotunde/Reuters)

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)