JEFFREY BROWN: And finally tonight, Margaret Warner has been in Mexico all week as that nation prepares to vote for a new president on Sunday.
In her reporting, she visited Juarez, the site of so much violence, and met a photographer who's been documenting the city's struggles.
A warning: Some of the images are disturbing.
JULIAN CARDONA, photographer: These photographs come from postcards, enlarged postcards of the old Juarez. This is the city I knew when I was a child. During those years, the city was a small place and I knew all the city. We grew up together.
MARGARET WARNER: Burritos Tony claims to have invented that staple of Mexican cuisine, and it's where photojournalist Julian Cardona took us to see what Ciudad Juarez once was, a lively but comfortable place hard by the Rio Grande River across from El Paso, Texas.
His parents moved here with him in 1960 from farther south, as so many others did, looking for the plentiful jobs on the border in U.S.-owned factories known as maquiladoras.
Fed up with his own humdrum work in the plants, in 1993, he joined a local newspaper, El Diario, as the city was growing by 50,000 a year.
JULIAN CARDONA: By the '90s, the whole city had several industrial parks and hundreds of plants. A TV set was made every three seconds, and a computer was made every seven seconds.
I was interested since the beginning to show the growing economy, underground economy in the city.
MARGARET WARNER: The new arrivals put up dwellings anywhere they could, even cardboard houses with sewage canals behind them.
JULIAN CARDONA: In many cases were taking any kind of land to settle.
We are on the exact place where I took these pictures on mid-'90s. In the picture you would see the sunset.
MARGARET WARNER: Behind that mountain or hill?
JULIAN CARDONA: Mm-hmm. You see the one house, and one guy is working on his house.
During the '90s, I came here to cover the new settlements, during recent years, to cover murders. There were several women who were found in this area.
MARGARET WARNER: Hundreds of Juarez women have been murdered over the last two decades, their bodies dumped on city streets or discovered in the vast desert beyond outside or never found at all.
Cardona saw the chaos coming. He shot these photographs in 1995, as the economy boomed and homicides began to surge.
JULIAN CARDONA: This photograph was taken on the boundary of two warring gangs in one barrio. In some way, I saw it coming. The city was growing in a chaotic way, and that wasn't sustainable for any society.
MARGARET WARNER: Two years later, a turning point.
JULIAN CARDONA: The story begins here, the first public killing in the history of the city.
MARGARET WARNER: Six people executed gangland-style in a restaurant after a bullfight downtown.
JULIAN CARDONA: It was the biggest massacre of all the history of the city, six people. It was very big news. During that time, many people were not aware that the city was becoming more chaotic little by little, and that the drug business was growing.
MARGARET WARNER: Growing because of the proximity to the United States and its giant illicit market, growing because it promised vast and fast riches to people used to nothing.
JULIAN CARDONA: What we have seen is the underground economy was developed during into the economy of crime, first drugs, in recent years have been kidnapping, extortion, house-jacking, carjacking. You get a job when you are a kidnapper. You get a job when you kill somebody for $100 or $200.
It's an economy. It's harder to eradicate this kind of economy than just a couple of gangs warring against each other.
MARGARET WARNER: Before long, the gangs weren't just killing each other, but preying on ordinary people, kidnapping for ransom and extortion.
JULIAN CARDONA: There were a lot of people who decided to cross the border to save their lives. And, like you see that pharmacy? It's closed. Photo studio, it's closed. You see many other -- some other places closed?
MARGARET WARNER: Army troops arrived in 2008, but the violence only grew. More than 3,600 people were killed in 2010. That year saw particularly grisly mass murders within months of each other, some 30 teenage students felled by bullets at birthday parties.
JULIAN CARDONA: During the recent years, we have had more than 10,000 homicides. And for three or four years, we have been rated as the most violent city on Earth.
MARGARET WARNER: Murders in Juarez did drop last year to just under 2,000. And last month, the city posted the lowest body count in years, still, one murder every 10 hours.
Sitting in Burritos Tony, Cardona says he wouldn't think of accepting offers to move elsewhere.
JULIAN CARDONA: I'm staying because this is my city. It's an important story, how a city becomes the most violent city on Earth. I was able to do it, and I'm OK with that. It's my job.
MARGARET WARNER: He takes us to the end of that story for all too many.
JULIAN CARDONA: We are at the municipal cemetery, San Rafael Cemetery. And this place is what is known as (SPEAKING SPANISH) the mass grave.
MARGARET WARNER: Who is buried here?
JULIAN CARDONA: Those who are not recognized by their relatives. At some point, when the morgue is packed with bodies, they decide to send the individual persons to the mass grave.
MARGARET WARNER: But we do see some crosses here. There are some marked areas.
JULIAN CARDONA: I think those -- at certain times, there are people who are so afraid even to have a funeral for their relative, and they avoid identifying the body. And after a certain time, they go and find a place where the body is found, and they put a cross.
MARGARET WARNER: And so they are still adding bodies here?
JULIAN CARDONA: They are still adding bodies here.
MARGARET WARNER: And in these sand dunes south of Juarez, there's still plenty of space to fill.