It's a sentiment shared by police in Dallas' suburban neighbors.
"We're not seeing a lot of crime directly attributable to MS-13 members. It's minimal," said David Tull, spokesman for the Irving Police Department. "We're not in denial. We know they're out there.
"We hear on the street that someone is coming in and we'll see graffiti around town, but unless we can get them in the light at the right time, we don't get a chance to get them."
Said Patrick Murphy of the Carrollton police: "It's really difficult to say how many MS-13 gang members we have. ... They come and go constantly."
That fluidity -- members moving among cliques and back and forth to Central America -- makes it hard to pin down numbers in any community with any accuracy, police said.
"This is a gang that operates across borders. It's common to see members of the L.A. clique work in El Salvador, or Salvadoran members operating in New York, recruiting or sharing tactics," said Brian Trucheon, director of the FBI's MS-13 National Gang Task Force, created in 2004. "The scary thing for us is how quickly they can evolve to move around obstacles law enforcement throws up."
MS-13 began in the Ramparts section of Los Angeles in the mid-1980s to protect refugees of El Salvador's civil war from other street gangs. Mara Salvatrucha is street slang for "Salvadoran guard posse." The tattoos gang members use as a mark of identity and pride invariably involve the initials MS and the number 13, a designation of an earlier alliance with a Southern California gang.
A 2005 Department of Homeland Security gang threat assessment identified MS-13 as one of the largest and most violent gangs in the country. That February, Immigration and Customs Enforcement agents launched a national sweep -- Operation Community Shield -- targeting MS-13 members. It was later expanded to include other violent gangs. More than 3,000 gangsters were eventually rounded up, one third of them affiliated with MS-13.
The gang's terrifying reputation includes a callous disregard for life and a willingness to use extreme violence with weapons ranging from machetes to semi-automatic rifles.
"Machetes, decapitations and sexual violence against victims are a common tool of intimidation," said Alonzo Pena, the ICE special agent in charge for South Texas. "They are growing rapidly and pose a significant risk to our communities. This is a gang we can't allow to continue to grow."
As a policy, ICE agents conduct face-to-face interviews with any member of the group arrested in Texas in an attempt to gather detailed intelligence.
One sign of the group's increased organization: Recently, MS-13 leaders have told members to remove tattoos from their faces, necks and arms to avoid notice from law enforcement. During interviews with agents, MS-13 members now deny involvement and insist their tattoos are residue of past involvement.
"We're sure that's just disinformation they're feeding us," Mr. Pena said. "The rule of MS-13 is once in, always in."
Houston, with its large Central American immigrant community, is the group's center of activity in Texas, authorities said.
"It doesn't surprise us that they are coming in greater numbers across the border," said Shawna Dunlap, an FBI special agent in Houston. She said Houston saw an increase in what she called "high-profile" gang activity last year, including extortion, robbery and kidnapping.
"About 50 percent of those we see in Houston have been deported multiple times," she said.