Known for its horrific murders, in which victims are set upon with machetes and baseball bats, it has a reach that now extends from its base in Central America into 40 US states as well as Mexico, Canada and Spain.
"MS-13 is a very well-known criminal brand," says Samuel Logan, author of a book on the gang. "It's a brand that creates fear and they use fear as a weapon."
And Donald Trump, whose administration has declared MS-13 a national security threat, has seized on that fearsome brand to justify stepped up deportations of undocumented immigrants, a border wall and pressure on so-called "sanctuary cities" to stop protecting vulnerable migrants.
MS-13 has "literally taken over towns and cities of the United States," Trump said last week, arguing that the border wall is needed to keep gang members out.
"MS-13 is going to be gone from our streets very soon, believe me," he said on another recent occasion.
The US Immigration and Customs Enforcement agency this month announced the arrests of nearly 1,100 gang members or associates. But two-thirds of those arrested were US citizens, not immigrants, and only 104 were members of MS-13.
Last week, Los Angeles police arrested 21 members of MS-13 -- a dozen of whom were gang leaders -- and charged 44 people in the city's biggest ever operation against the group.
Two birds with one stone
Hector Silva, a Salvadoran with Insight Crime, a research group that focuses on organized crime in Latin America, says the gang is the perfect foil for Trump's policies.
MS-13, he says, kills two birds with one stone for Trump: "In the minds of Americans, gangs are Latin American, hence they are both bad and foreign," Silva says.
But experts and law enforcement officials warn that the strategy could make combating MS-13, or Mara Salvatrucha as the gang is also known, more difficult.
Police say undocumented Hispanics are the victims in nearly all MS-13 crimes, and Trump's anti-immigration policies keep them from coming forward with information about the violence, for fear of being deported.
New York's Suffolk County was the scene of a brutal murder in April of four young men, whose mutilated bodies were found dumped in a wooded area in the town of Central Islip.
One was 16 years old, two were 18 and the fourth was 20 -- and the extreme violence with which they were killed pointed to MS-13.
But the county's police commissioner, Timothy Sini, told a US Senate hearing this week that cracking down on illegal immigrants is not helping police investigators.
"If individuals believe that they cannot freely cooperate with law enforcement because of their immigration status, the mission of the police department and the safety of all residents are compromised," Sini said.
"They can live with the gang, as cruel as it is, but not with deportation," he said.
A vicious circle
MS-13 emerged in the 1980s in the streets of Los Angeles among Salvadoran immigrants who had fought in their country's brutal civil war.
The gang caught on, and its ranks spread to other Central American immigrants.
In the 1990s and 2000s, many gang members were deported to El Salvador, Guatemala and Honduras, where they gained immense power, turning Central America's northern triangle into the world's deadliest region not at war.
Many then returned to the United States, strengthened by their organizational base in Central America.
Today, MS-13 has a presence across the US, and has become expert at smuggling deportees back into the country.
It also is exploiting the vulnerability of the thousands of Central American minors who cross the border alone.
"We're concerned that MS-13 is recruiting younger people," said Sini. "In one instance, a 10-year-old."
The average age of the gang members arrested in Suffolk County, which encompasses the eastern end of Long Island, is 18, he said.
MS-13 is not a big drug trafficking cartel, like the powerful Colombian and Mexican crime groups. Instead, it finances itself with street sales of drugs, extortion, human trafficking and sometimes prostitution.
It was declared a "transnational criminal organization" in 2012 by the United States.
"I don't think that MS-13 is a security threat to the United States ... but rather a threat to the security of Hispanic communities," said Silva.
"Where they truly are a national security threat is in El Salvador," he said.
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