Reproduction of a letter to the National Commission of Human Rights from criminals, drug dealers, murderers and kidnappers in "El Altiplano," Mexico's highest-security prison. Ronaldo Schemidt/AFP/Getty Images hide caption

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Julio Cesar Chavez at his home in Tijuana, Mexico. Carrie Kahn/NPR hide caption

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A platform owned by Mexico's state-run oil company Pemex is seen off the Bay of Campeche in the Gulf of Mexico. The country has recently opened up its energy sector to foreign investors. Victor Ruiz/Reuters/Landov hide caption

itoggle caption Victor Ruiz/Reuters/Landov

The alleged leader of the Zetas drug cartel, Omar Trevino Morales, is taken under custody to be presented to the press at the Attorney General Office's hangar at the airport in Mexico City, on March 4. Mexican authorities captured Trevino Wednesday, dealing a blow to the feared gang and giving the embattled government a second major arrest in a week. Omar Torres/AFP/Getty Images hide caption

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The 2,100-person Tijuana municipal police force is one of Mexico's largest. It's also the first in the country to employ body cameras for its officers. Washington Post/Getty Images hide caption

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In 2013, the U.S. imported about 2 million tons of Coronas and Modelos, making beer Mexico's largest agricultural export to the U.S., according to a USDA report. Scott Olson/Getty Images hide caption

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Mexico's President Enrique Pena Nieto gestures after delivering a speech at the Los Pinos presidential Palace in Mexico City on Tuesday. Yuri Cortez /AFP/Getty Images hide caption

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In this video frame grab image taken from Milenio TV via APTN, police look at the scene where a gas tank truck exploded outside a maternity and children's hospital in Mexico City on Thursday. AP hide caption

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Jasjit Kaur Singh, an Indian chef, cooks kaala channa, a traditional spicy Sikh dish. A psychologist says that children who grow up in cultures with lots of spicy food are taught to like spice early on. Richard Lautens/Toronto Star via Getty Images hide caption

itoggle caption Richard Lautens/Toronto Star via Getty Images

La Roca restaurant in Nogales, Mexico, draws a mix of American tourists and locals. It used to have an American bank account and credit card until the bank closed the account. Jude Joffe-Block/KJZZ hide caption

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Pablo Cote holds a photo of his deceased father of the same name in July 2013 in Tlaxcala, Mexico. Cote was kidnapped while driving back from the U.S. border to the east-central state of Tlaxcala. He was beaten to death, part of the mass killing of 193 bus passengers and other travelers by the Zetas. Ivan Pierre Aguirre/AP hide caption

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Relatives of 43 students who went missing in Iguala, Mexico, search for them on a hill on the outskirts of town on Nov. 29. After the students vanished, searches around Iguala have turned up nearly a dozen clandestine graves. None of the remains found in those mounds belonged to the students. Eduardo Verdugo/AP hide caption

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Maria Isabel de la Paz, a U.S. citizen, was twice turned away when trying to enter the U.S. legally. When she attempted an illegal crossing, her case was decided by a Border Patrol agent, not an immigration judge. John Burnett/NPR hide caption

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Natividad de la Cruz Bartolo shows a picture of her son, Emiliano, one of 43 university students who went missing months ago. Carrie Kahn/NPR hide caption

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A woman walks toward the international crossing gate in Nogales, Ariz., in March 2013. Jahi Chikwendiu/Washington Post via Getty Images hide caption

itoggle caption Jahi Chikwendiu/Washington Post via Getty Images