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

Nabor, a small-scale marijuana grower in the northwestern Mexican state of Sinoloa, checks his plants. As legal pot increasingly becomes available in the U.S., Americans appear to be buying more that is grown domestically. Prices for marijuana from Mexico have fallen sharply. John Burnett/NPR hide caption

itoggle caption John Burnett/NPR

Mexico's Attorney General Jesus Murillo Karam addresses a news conference in Mexico City on Friday. He announced the arrest of three suspects in the brutal slaying of 43 students in the country's south. Mario Guzman/EPA/Landov hide caption

itoggle caption Mario Guzman/EPA/Landov

Dubbed the "imperial couple" by a Mexican newspaper, the mayor of Iguala, Jose Luis Abarca, and his wife Maria de los Angeles Pineda were wanted for questioning in the case of the missing students and the mass graves found near Iguala. They are shown here in a photo taken in May. Alejandrino Gonzalez/AP hide caption

itoggle caption Alejandrino Gonzalez/AP

Jill Tahmooressi stands outside the Mexican Consulate in Miami, in May to protest the arrest of her son in Mexico. He was released by a federal judge in Mexico today. J Pat Carter/AP hide caption

itoggle caption J Pat Carter/AP

Three large crosses lean against the burned out facade of Iguala's City Hall. Masked protesters angry about the disappearance of 43 students — attacked on orders of Iguala's mayor, according to Mexican federal authorities — burned the building last week. Carrie Kahn/NPR hide caption

itoggle caption Carrie Kahn/NPR

Elaborately decorated skulls are crafted from pure sugar and given to friends as gifts. The colorful designs represent the vitality of life and individual personality. Karen Castillo Farfán /NPR hide caption

itoggle caption Karen Castillo Farfán /NPR

In Mexico City on Wednesday, people march to demand justice for 43 missing students. Mexican authorities ordered the arrest of the mayor of Iguala and his wife in connection with the attack. Yuri Cortez/AFP/Getty Images hide caption

itoggle caption Yuri Cortez/AFP/Getty Images

Students chant slogans in front of the Attorney General Office in Mexico City on Wednesday during a protest over the 43 students missing in Iguala, Guerrero State. Omar Torres/AFP/Getty Images hide caption

itoggle caption Omar Torres/AFP/Getty Images

Groups of rural and community police arrive in the city of Iguala on Tuesday to help in the search for 43 students who disappeared after a confrontation with local police on Sept. 26. Miguel Tovar/STF/LatinContent/Getty Images hide caption

itoggle caption Miguel Tovar/STF/LatinContent/Getty Images

A woman wears a black veil and carries a cross reading in Spanish "Assassin State," as thousands march down one of the capital's main boulevards to demand that the government find the 43 students who disappeared in southern Guerrero State. Rebecca Blackwell/AP hide caption

itoggle caption Rebecca Blackwell/AP

Relatives of students reported missing after a violent confrontation in Iguala with police, pass the time near a makeshift altar as they wait for news of their loved ones at the Isidro Burgos rural teachers college in Ayotzinapa, Mexico. Eduardo Verdugo/AP hide caption

itoggle caption Eduardo Verdugo/AP

President Johnson and Mexican President Gustavo Di­az Ordaz, with their wives, celebrate the dedication of the Chamizal Monument in Juarez, Mexico, on Oct. 28, 1967. The monument signified the international boundary marker between the two countries, designated in 1964. Yoichi Okam/Courtesy of the LBJ Presidential Library hide caption

itoggle caption Yoichi Okam/Courtesy of the LBJ Presidential Library