PHOENIX -- The fastest-growing gang in the world is coming to Arizona -- a trend that makes federal agents along the U.S.-Mexico border uncomfortable.

Mara Salvatrucha, or MS-13, is known for its violence and guerilla warfare training, experts said.

"They're pretty ruthless," said Agent Mike Scioli of the U.S. Border Patrol. "And killing somebody means nothing to them."

MS-13 comes from El Salvador, with an estimated 100,000 members throughout Latin American and the U.S., but gang members are crossing the border in greater numbers.

"From Oct. 1 until the end of July we've seen over 50 different people involved in not only MS-13, but a number of different gangs affiliated with them," Scioli said. "Just in the past week we've had five."

According to law enforcement personnel, MS-13 members come to Arizona because its position on the border makes it a hot spot for drugs and human smuggling.

Though many MS-13 members are caught crossing the border illegally, some do make it to the Valley.

"They're everywhere," said Maricopa County Sheriff's Deputy John Hansen. "They should worry about them. These guys are not just in the slums; they're in every neighborhood. You can find them from Apache Junction all the way to West Phoenix and everywhere in between."

Border agents are not the only people who are cautious about the gang; illegal immigrants also fear MS-13. Ariel Vasquez, a man who crossed the border illegally, said it is the most dangerous gang on the streets.

"They are very organized," Vasquez told 5 Investigates through a translator. "They have spread all over the United States and Mexico and Central America."

Back on the border, agents try to keep the gang members from crossing into the U.S.

"You always keep that in the back of your head," Scioli said. "One of these guys could be part of that group."

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