Sheriff officers from San Diego's North County Transit District approach a commuter train while training for an active shooter scenario onboard a train in Oceanside, California December 10, 2014. (Photo by Mike Blake/Reuters)

Sheriff officers from San Diego's North County Transit District approach a commuter train while training for an active shooter scenario onboard a train in Oceanside, California December 10, 2014. (Photo by Mike Blake/Reuters)

Sheriff officers from San Diego's North County Transit District help a man, acting as a scripted injured victim, leave a transit train while training for an active shooter scenario in Oceanside, California December 10, 2014. (Photo by Mike Blake/Reuters)

The gun of a sheriff officer from San Diego's North County Transit District is seen as a team of police sweep a commuter train while training for an active shooter scenario onboard a train in Oceanside, California December 10, 2014. (Photo by Mike Blake/Reuters)

A sheriff officer from San Diego's North County Transit District holds a fake gun during an active shooter scenario while training in Oceanside, California December 10, 2014. (Photo by Mike Blake/Reuters)

A street performer dressed as the Statue of Liberty stands amongst light snow in Times Square in New York December 10, 2014. Snow showers fell in the region through Wednesday and should clear early Thursday. (Photo by Andrew Kelly/Reuters)

An Ayotzinapa Teacher Training College student writes graffiti in the Institute of Parliamentary Studies of the Guerrero State Congress, as part of a protest demanding justice for the 43 missing students of the Ayotzinapa Teacher Training College Raul Isidro Burgos, in Chilpancingo, in the Mexican state of Guerrero, December 10, 2014. Mexico said at the weekend that mounting evidence and initial DNA tests confirmed that the students were incinerated at a garbage dump by drug gang members. The graffiti reads “Don't forget, don't forgive”. (Photo by Jorge Dan Lopez/Reuters)

A man, who was beaten up by residents, sits guarded by two police officers in the back of a police truck in Xalapa, Mexico, December 10, 2014. The man, accused of being part of a group of people who had kidnapped an 11-year-old school girl, was grabbed from a car, as the group tried to flee the area, by infuriated neighbors who beat him up until the police arrived, according to local media. (Photo by Oscar Martinez/Reuters)

The polluted area caused by an oil spill is seen at the Evrona desert reserve, near the Red Sea resort city of Eilat December 10, 2014. Ecologists said on Wednesday it could take years to clean up the massive oil spill that flooded an Israeli nature reserve with up to five million litres of crude and threatened to spread to the Red Sea shore and neighbouring Jordan. (Photo by Baz Ratner/Reuters)

Cuban security personnel detain a member of the Ladies in White group during a protest on International Human Rights Day, in Havana December 10, 2014. Cuban police detained several activists during peaceful demonstrations at a popular Havana square on Wednesday, an annual protest on International Human Rights Day. (Photo by Enrique De La Osa/Reuters)

Cuban security personnel detain a supporter of the Ladies in White group during a protest on International Human Rights Day, in Havana December 10, 2014. (Photo by Enrique De La Osa/Reuters)

Copies of the French Civil Code are placed amongst a frieze depicting the “Oath of the Jeu de Paume” (June 20, 1789) on the Republic statue as French lawyers, notaries and bailiffs attend a national protest against a government reform plan to deregulate their profession in Paris December 10, 2014. The Macron bill, presented as “Law on Growth and Activity” plan, includes loosening of barriers to entry in highly regulated professions ranging from notaries to bailiffs. The bill aims to stimulate competition, leading to cheaper services in areas where these groups currently have virtual monopolies. (Photo by Charles Platiau/Reuters)

A woman poses for pictures among panda installations during an exhibition in Hefei, Anhui province, December 10, 2014. (Photo by Reuters/Stringer)

A man moves a panda installation during an exhibition in Hefei, Anhui province, December 10, 2014. (Photo by Reuters/Stringer)

A man walks past burning houses after a fire broke out at a slum area in Manila December 11, 2014. Around 200 houses were gutted by the fire in the early morning of Thursday, which left an estimated 500 families homeless and one firefighter injured, local media reported. (Photo by Romeo Ranoco/Reuters)

Families carry their belongings as they evacuate their homes after a fire broke out at a slum area in Manila December 11, 2014. (Photo by Romeo Ranoco/Reuters)

A woman walks past election posters for Japan's upcoming snap election in Tokyo, December 11, 2014. Pictured bottom left and bottom right is Japan's Prime Minister and leader of the ruling Liberal Democratic Party (LDP) Shinzo Abe. (Photo by Thomas Peter/Reuters)

Christmas decorations light up the Medellin river in Medellin, Colombia, December 10, 2014. (Photo by Fredy Builes/Reuters)

Frost covers the mask and part of the hat of a soldier of the People's Liberation Army (PLA) as he stand guard near the border of China and Russia in Heihe, Heilongjiang province December 10, 2014. The local temperature reached -32 degrees Centigrade (-25.6 degrees Fahrenheit) on Wednesday. (Photo by Reuters/Stringer)

Fishermen sell spotted eels in Alexandria, Egypt, December 11, 2014. (Photo by Asmaa Waguih/Reuters)

Cui Juguo, 50-year-old security guard, balances an ostrich egg on a needle in Changsha, Hunan province December 10, 2014. Cui has practiced balancing eggs on needle for over 6 years and he once succeeded balancing three eggs within a minute on a local television program, local media reported. (Photo by Darwin Zhou/Reuters)

A policeman takes pictures as he rides on a motorcycle towards a workers' rally in Tangerang, December 11, 2014. Hundreds of workers held the protest demanding the government to raise minimum wages after the government's decision to raise subsidized fuel price, local paper reported on Wednesday. (Photo by Reuters/Beawiharta)

An undercover police officer, who had been marching with anti-police demonstrators, aims his gun at protesters after some in the crowd attacked him and his partner in Oakland, California December 10, 2014. Police said more than 100 demonstrators marched in Berkeley, California, which has a history of social activism. Under cloudy skies, turnout was smaller than earlier in the week, when demonstrators in the area threw rocks at police and shut down a major freeway. (Photo by Noah Berger/Reuters)

A police officer holds back anti-police demonstrators as an undercover officer makes an arrest in Oakland, California December 10, 2014. (Photo by Noah Berger/Reuters)

Vietnamese fans, dressed in the colours of their national flag, cheer before the second leg of their ASEAN Football Federation Suzuki Cup 2014 semi-final match against Malaysia at My Dinh stadium in Hanoi December 11, 2014. (Photo by Reuters/Kham)

Protesters rallying against police violence storm a lecture with PayPal co-founder Peter Thiel at the University of California at Berkeley campus in Berkeley, California December 10, 2014. Police said more than 100 demonstrators marched in Berkeley, California, which has a history of social activism. Under cloudy skies, turnout was smaller than earlier in the week, when demonstrators in the area threw rocks at police and shut down a major freeway. (Photo by Noah Berger/Reuters)

Bollywood actress Sonam Kapoor (R) helps Russian President Vladimir Putin (L) to light a traditional Indian oil lamp as India's Prime Minister Narendra Modi watches during the inauguration of World Diamond Conference in New Delhi December 11, 2014. Modi told Putin on Thursday that Russia will remain India's top defence supplier, even though New Delhi's options had improved since the end of the Cold War. (Photo by Ahmad Masood/Reuters)

The laser weapon system (LaWS) is tested aboard the USS Ponce amphibious transport dock during an operational demonstration while deployed in the Gulf in this November 15, 2014 U.S. Navy handout photo provided December 11, 2014. The weapon system has performed beyond expectations in four months of operational testing, the chief of Navy research said on Wednesday, lifting hopes for a new U.S. defense against cheap anti-ship arms. The intended use of the LaWS is ship-defense against drones or small-boat attackers; the LaWS at present is not designed to engage incoming missiles, large aircraft, ships, or submerged objects. LaWS utilizes a solid-state infrared beam which can be tuned to high output to destroy the target or low output to warn or cripple the sensors of a target. Among the advantages of this device versus projectile weapons is the low cost per shot, as each firing of the weapon requires only the minimal cost of generating the energetic pulse; by contrast ordnance for projectile weapons must be designed, manufactured, handled, transported and maintained, and takes up storage space. (Photo by John Williams/Reuters/U.S. Navy)

The laser weapon system (LaWS) is tested aboard the USS Ponce amphibious transport dock during an operational demonstration while deployed in the Gulf in this November 15, 2014 U.S. Navy handout photo provided December 11, 2014. (Photo by John Williams/Reuters/U.S. Navy)

Explosions are seen as the national flags of Israel (front L) and the U.S. are placed on the ground during a military drill by Palestinian Islamic Jihad militants in the southern Gaza Strip December 11, 2014. (Photo by Suhaib Salem/Reuters)

A man dressed as Father Frost walks with Siberian Huskies in a park during an annual Christmas Fair in Krasnoyarsk, Siberia, December 11, 2014. (Photo by Ilya Naymushin/Reuters)

Women use their mobile phones next to a stuffed Mickey Mouse toy as they sit in a bench outside a commercial mall in Santiago city, December 10, 2014. (Photo by Ivan Alvarado/Reuters)

A man uses a sickle to dig in an attempt to uproot the remains of an olive tree in the besieged town of Arbeen in the eastern Ghouta of Damascus December 11, 2014. Due to fuel and electricity shortages, residents of Arbeen are cutting down trees for firewood to be sold and used for cooking, heating and business. (Photo by Diaa Al-Din/Reuters)

A pedestrian leaps over a rain puddle at the Embarcadero in San Francisco, California December 11, 2014. A Pacific storm lashed northern and central California on Thursday with heavy rain and high winds, knocking out electricity to tens of thousands of homes, disrupting commercial flights and prompting school closures in the San Francisco Bay area. (Photo by Robert Galbraith/Reuters)

People look at a car hanging on the edge of a caved-in area on a street in Zhenjiang, Jiangsu province December 12, 2014. The street collapsed on Friday morning as the car drove by and formed the pit measuring 2m (6.7ft) in depth and 5m (16.4ft) in diametre, according to local media. (Photo by Reuters/Stringer)

A Ford sedan car halts on the verge of a five meters wide and two meters deep hole at Yunlianghe Road on December 12, 2014 in Zhenjiang, Jiangsu Province of China. A Ford sedan car halted on the verge of a hole at Yunlianghe Road after the road collapsed and formed a five meters wide and two meters deep hole abound 8 o'clock on Friday morning. The road was just opened for two years and the reason is still under investigation. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)

Cast member Diana Bang poses during the premiere of the film “The Interview” in Los Angeles, California December 11, 2014. (Photo by Kevork Djansezian/Reuters)

A labourer uses a ladder at the construction site of a bridge being built over the river Yamuna for metro rail in New Delhi December 12, 2014. With growth struggling at 5.3 percent in the July-September quarter, it is likely to be some time before India recaptures the 8 percent growth levels needed to create enough jobs for a rapidly expanding workforce. (Photo by Anindito Mukherjee/Reuters)