JOHN CARLOS FREY: Miguel Angel Gomez, a 30-year-old taxi driver here in El Salvador spends a lot of time looking in his rear-view mirror, worried that he'll be the next victim of a notoriously violent street gang that already murdered Miguel's brother.

A local news report showed the scene of the crime.

MIGUEL ANGEL GOMEZ: First they shot him and then they beheaded him. Here if they don't like you or for any little thing, they have you killed.

JOHN CARLOS FREY: Miguel says his brother was not part of a gang and has no idea why his brother was killed. But Miguel says gang members are now after him because they believe that he'll seek revenge.

What happens to you and your wife if you both stay here in El Salvador?

MIGUEL ANGEL GOMEZ: They will kill us.

JOHN CARLOS FREY: He and his wife are now planning to illegally cross the border into Texas, where they have relatives. Since last January more than 230,000 undocumented Central Americans, many of them children, have crossed into the United States fleeing violence perpetrated by gangs and drug cartels in countries like El Salvador, Honduras, and Guatemala.

With all the reporting about the current crisis, what's little understood is that the mass exodus to the United States earlier this year was actually thirty years in the making. Fueled by American foreign policy decisions in the 1980's and an act of congress in the mid 1990's.

AL VALDEZ: There are experts who say this is all Americans' fault and there are those who say it's not our fault because we're following the rules. And then there's people like me sort of on the fence.

JOHN CARLOS FREY: It all began in the early 1980's when El Salvador was in the midst of a brutal civil war. It was the height of the cold war and the Reagan administration, fearful of communist expansion in Central America supported the military-backed government with arms and financing. Seventy-five thousand were killed in the conflict, mostly at the hands of government forces. It's estimated that hundreds of thousands of Salvadorans fled their war-torn country seeking refuge in the United States.

AL VALDEZ: The mass exodus of Salvadorians to flee the conflict down there put a large population of Salvadorian immigrants in Los Angeles.

Al Valdez is a 28-year veteran of the police force in Orange County, California, who specialized in undercover field operations and headed the gang investigation unit for the Attorney General's office there. He explains that many of these Salvadoran families lived in poverty in the rough neighborhoods around downtown Los Angeles. Some of these new immigrants joined Latino gangs like 18th street gang and Mara Salvatrucha 13, or MS 13, for both protection and a livelihood.

AL VALDEZ: Kids join gangs as a mechanism to survive. Now granted your life sucks, but at least you're alive and you have food and water, and you have protection.

JOHN CARLOS FREY: Many of those Salvadoran gang members ended up in California prisons. And this is where that act of congress comes in. Before 1996, only criminals convicted of violent felonies with sentences of five years or more could be deported. But all that changed in 1996, when in an attempt to get tough on illegal immigration, congress passed a law allowing authorities to deport criminals if they had a prison sentence of just one year.

This led to the deportation of 10s of thousands of gang members to Central America, many to El Salvador. Once they arrived they set up shop here and recruited local Salvadorans into the gangs. Many of the new recruits were teenagers who joined for the money and for the street cred. Others because they'd been threatened that if they refused to join, they'd be killed.

AL VALDEZ: Those countries, Central America, was ripe for a criminal culture to overtake it because of its severe poverty and the lack of opportunities, the corruption involved. It was like a Petri dish that you put an Ebola virus in it and it's going to grow like crazy.

CARLOS PONCE: We had a pretty, potentially grave crime problem represented by these gang members that are being deported and a very young police force that was going to have to deal with it.

JOHN CARLOS FREY: Carlos Ponce, a prominent Salvadoran crime analyst and former director of research for the national police force says the country was unprepared for this wave of gang members who had cut their teeth on the streets of Los Angeles. To make matters worse, Ponce says, when these deportations started U.S. authorities were providing no information about who was heading their way.

Wait a minute. So, the U.S. was deporting criminals without their criminal records?

CARLOS PONCE: Yeah. Yeah.

JOHN CARLOS FREY: You didn't know who was coming into the country?

CARLOS PONCE: We didn't know who was coming and you know, they were free to do as they pleased.

JOHN CARLOS FREY: While Ponce says that coordination with the United States has improved, deportations of gang members continue to this day.

So how much responsibility do you give the United States for the gang problem in El Salvador?

AL VALDEZ: I think the U.S. responsibility should've been, or could be, that we should advise the local officials in the countries of repatriation of exactly who we're sending back. That this guy was arrested for murder. He did time for murder. This guy was arrested for robbery. He's a sexual predator. We're sending ‘em back. You need to have this data to make your country safe.

JOHN CARLOS FREY: Immigration and Customs Enforcement told us that, “The removal of known violent criminal gang members and foreign fugitives are among the agency's highest enforcement priorities. During the removal process, ICE works closely with foreign governments to … share all relevant information about individuals being returned, to include their criminal history.”

JOHN CARLOS FREY: Were you a bad kid?

MANUEL FLORES: I was pretty bad. To this time now, I'm still bad.

32-year-old Manuel Flores, also known as “Sad Boy” by fellow gang members in Los Angeles was deported from a federal prison to El Salvador just about a two years ago. Flores recounted his days in rough South Central L.A.

MANUEL FLORES: Gangbang on the rival from a different hood.

JOHN CARLOS FREY: Are you talking about violence?

MANUEL FLORES: Uh-huh.

JOHN CARLOS FREY: Beating people up?

MANUEL FLORES: Yeah.

JOHN CARLOS FREY: Shooting people? Killing people?

MANUEL FLORES: Uh-huh.

JOHN CARLOS FREY: So you were involved with people who were killing other people?

MANUEL FLORES: Yeah. Yes.

JOHN CARLOS FREY: Flores's story embodies this 30-year cycle of violence that led to what President Obama called a humanitarian crises along the U.S.-Mexico border this past summer. When he was only 6-months old, he and his family fled the civil war in El Salvador. He grew up in L.A., became a gang member, was imprisoned after stabbing someone in the neck and eventually deported back to El Salvador. Now he acknowledges that he is likely to resume his life of crime, crime that in part fueled last summer's mass migration.

JOHN CARLOS FREY: You want to go back to the streets?

MANUEL FLORES: If you want to make money for you and your people, I mean, you just go ahead and gangbang all your life.

CARLOS PONCE: The gang members are – stroll on the streets with their rifles showing. I mean, just out of the most exaggerated movie you can see about gangs in the most savage country you can imagine. And that's why at the end people are leaving the country, because their families and their kids don't have a chance against this monster that has been growing and growing for the last few years.

JOHN CARLOS FREY: In a country of just 6 million, there are now a reported 7 murders a day according to the U.S. State Department and a recent survey conducted here found that one out four Salvadorans has considered leaving the country due to violence and the lack of economic opportunity.

People are fleeing the country because they are afraid of you. They're afraid of the gangs.

SANTIAGO: It's clear man. I accept that.

JOHN CARLOS FREY: This high-level member of the 18th street gang, who asked to be called “Santiago,” also agreed to talk with us. Santiago said he knows all about Salvadorans, many of them children, fleeing to the U.S. to escape criminals like him and he's just fine with that.

SANTIAGO: It doesn't bother me. You know why? Why wouldn't I want a child that will become a gang member here to leave the country? Let him pick up and go and get reunited with his mother in the U.S. and have access to a quality education.

JOHN CARLOS FREY: The Salvadoran authorities tell us they are doing all they can to stop the violence and keep their citizens from fleeing to the U.S. But they say they are up against it. Twenty thousand officers trying to battle 60 thousand gang members. A raid on 18th street gang members in a hilltop village by the anti-gang task force illustrates the problem.

On a pitch black moonless night, we follow the officers into a wooded cliff-side area dotted with adobe homes. Using battering rams the officers raided multiple residents simultaneously. Despite meticulously planning the raid for two months, by the end of the evening police only arrested two of the ten suspected gang members they were looking for. Later they speculated that the gang members had been tipped off.

El Salvador's inability to defeat the gangs continues to fuel migration to the U.S., despite the 10s of millions of dollars a year the U.S. is now pouring into this Central American nation for both security and economic assistance. Remember taxi driver Miguel Angel Gomez, whose brother was decapitated by gang members? Lately, he says, they've been following him as he drives his taxi.

MIGUEL ANGEL GOMEZ: I feel that the more time passes, the closer they get.

JOHN CARLOS FREY: Which is why after requesting and being denied asylum in the United States, he's still planning to go to the U.S. illegally. He's not the only one in our story heading to America. Manuel Flores, the gang member the United States sent back to El Salvador says he planning to return, too.