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  • ABC News "Nightline" went into the world of gangs in El Salvador, exploring the violence that keeps communities there living in constant fear and the impact of these deadly gangs as they spread north into the United States. Watch the full story on "Nightline" on May 17. Shown here, a prison outside San Salvador that holds inmates only from the 18th Street Gang; 169 members of its Revolucionario faction are packed into three cells.
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  • These are members of the Sureños faction of the 18th Street Gang. They are separated from the Revolucionarios because if they are kept in the same cell, they say they will kill each other. These inmates are chained to a metal pipe and are released only twice a day to use the bathroom.
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  • An 18th Street Gang member who goes by the name Clavo, which means "nail." He is the leader of an area known as La Fosa (the Graveyard). He says this is where many bodies were dumped during El Salvador's 12-year civil war in the late 1980s, which left 75,000 people dead.
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  • Cesar is a member of the West Side 18th Street Gang in a neighborhood known as Ciudad Delgado (Skinny City) in San Salvador. He spent 14 years in Los Angeles before being deported back to El Salvador. The tattoo on his chest reads "666," the number of the beast.
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  • Cesar shows off his back tattoo, which shows his allegiance to the Shatto Park Locos, a clique in the Koreatown neighborhood of Los Angeles.
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  • Inside a destroyer house, or hideout, for an 18th Street Gang clique in San Salvador.
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  • An 18th Street Gang leader known as Santiago shows off his back tattoo. He is the main spokesman for all the gangs of El Salvador, including MS-13, the 18th Street Sureños and the 18th Street Revolucionarios.
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  • A member of the anti-gang unit, or "antipandillas," on patrol, looking for gang members and leaders in San Salvador. In August 2015, the Supreme Court of El Salvador declared the MS-13 and 18th Street gangs terrorist organizations.
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  • El Salvador's anti-gang unit searches for suspected gang members on the streets of San Salvador.
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  • Bodies of homicide victims inside Medicina Legal, San Salvador's morgue. Last year El Salvador became the murder capital of the world, with 104 homicides per 100,000 residents. That's more than 20 times the rate in the United States.
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  • A medical examiner from the city morgue collects the body of a 23-year-old homicide victim outside San Salvador.
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  • Bones from homicide victims at Medicina Legal. They are collected by forensic archaeologists from mass or unmarked graves, often from dismembered bodies.
    Adam Desiderio/ABC News
  • Family members and friends gather for the burial of Alexis, a 17-year-old who was killed by the MS-13 gang. Two months earlier, his older brother, Roberto, was killed by a gang, leaving their youngest brother, Jorje, the family's only surviving son.
    Adam Desiderio/ABC News