Others are skeptical about claims cartels are expanding their presence, saying law-enforcement agencies are prone to exaggerating threats to justify bigger budgets.
David Shirk, of the University of San Diego's Trans-Border Institute, said there is a dearth of reliable intelligence that cartels are dispatching operatives from Mexico on a large scale.
"We know astonishingly little about the structure and dynamics of cartels north of the border," Shirk said. "We need to be very cautious about the assumptions we make."
Statistics from the DEA suggest a heightened cartel presence in more U.S. cities. In 2008, around 230 American communities reported some level of cartel presence. That number climbed to more than 1,200 in 2011, the most recent year for which information is available, though the increase is partly due to better reporting.
Federal agents and local police say they have become more adept at identifying cartel members or operatives using wiretapped conversations, informants or confessions. Hundreds of court documents reviewed by the AP appear to support those statements.
"This is the first time we've been seeing it — cartels who have their operatives actually sent here," said Richard Pearson, a lieutenant with the Louisville Metropolitan Police Department, which arrested four alleged operatives of the Zetas cartel in November in the suburb of Okolona.
People who live on the tree-lined street where authorities seized more than 2,400 pounds of marijuana and more than $1 million in cash were shocked to learn their low-key neighbors were accused of working for one of Mexico's most violent drug syndicates, Pearson said.
One of the best documented cases is Jose Gonzalez-Zavala, who was dispatched to the U.S. by the La Familia cartel, according to court filings.
In 2008, the former taxi driver and father of five moved into a spacious home at 1416 Brookfield Drive in a middle-class neighborhood of Joliet, southwest of Chicago. From there, court papers indicate, he oversaw wholesale shipments of cocaine in Illinois, Wisconsin and Indiana.
Wiretap transcripts reveal he called an unidentified cartel boss in Mexico almost every day, displaying the deference any midlevel executive might show to someone higher up the corporate ladder. Once he stammered as he explained that one customer would not pay a debt until after a trip.
"No," snaps the boss. "What we need is for him to pay."
The same cartel assigned Jorge Guadalupe Ayala-German to guard a Chicago-area stash house for $300 a week, plus a promised $35,000 lump-sum payment once he returned to Mexico after a year or two, according to court documents.
Ayala-German brought his wife and child to help give the house the appearance of an ordinary family residence. But he was arrested before he could return home and pleaded guilty to multiple trafficking charges. He will be sentenced later this year.
Socorro Hernandez-Rodriguez was convicted in 2011 of heading a massive drug operation in suburban Atlanta's Gwinnett County. The chief prosecutor said he and his associates were high-ranking figures in the La Familia cartel — an allegation defense lawyers denied.
And at the end of February outside Columbus, Ohio, authorities arrested 34-year-old Isaac Eli Perez Neri, who allegedly told investigators he was a debt collector for the Sinaloa cartel.
An Atlanta attorney who has represented reputed cartel members says authorities sometimes overstate the threat such men pose.
"Often, you have a kid whose first time leaving Mexico is sleeping on a mattress at a stash house playing Game Boy, eating Burger King, just checking drugs or money in and out," said Bruce Harvey. "Then he's arrested and gets a gargantuan sentence. It's sad."
Typically, cartel operatives are not U.S. citizens and make no attempt to acquire visas, choosing instead to sneak across the border. They are so accustomed to slipping back and forth between the two countries that they regularly return home for family weddings and holidays, Riley said.