http://www.chron.com/disp/story.mpl/metropolitan/6909500.html

BROWNSVILLE — The Zapata County sheriff Thursday was questioning why a Mexican military helicopter was hovering over homes on the Texas side of the Rio Grande.

It was one of the more jarring incidents of the fourth week of border tensions sparked by drug killings — and rumors of drug killings — in the Mexican state of Tamaulipas.

Sheriff Sigifredo Gonzalez said he'd reviewed photos of the chopper flown by armed personnel Tuesday over a residential area known as Falcon Heights-Falcon Village near the binational Falcon Lake, just south of the Starr-Zapata county line. He said the helicopter appeared to have the insignia of the Mexican navy.

“It's always been said that the Mexican military does in fact ... that there have been incursions,” Gonzalez said. “But this is not New Mexico or Arizona. Here we've got a river, there's a boundary line. And then of course having Falcon Lake, Falcon Dam, it's a lot wider. It's not just a trickle of a river, it's an actual dam. You know where the boundary's at.”

The sighting came amid ongoing fighting between the Gulf Cartel and its former enforcers, Los Zetas. The mounting death toll and crisis of fear in cities opposite the Texas border have drawn global attention, as has a news blackout in affected cities with the kidnappings of eight Mexican journalists, at least one of whom was killed.

As violence continued Thursday with a highway shootout in the state of Tamaulipas, a Senate subcommittee in Washington heard testimony that drug cartels are trying to infiltrate U.S. agencies along the border, with corruption cases among Homeland Security personnel on the rise.

In the past two years, there have been 400 public corruption cases involving federal, state and local law enforcement agents originating from the Southwest border region, Kevin Perkins, FBI assistant director for criminal investigations, told the Senate Homeland Security subcommittee on preparedness.

In addition to the highway battle, news from Tamaulipas on Thursday included a 25-year-old man found dead on a roadside in Miguel Alemán. On Wednesday, three people died in two gunbattles in Reynosa.

Four other deaths have been reported since Saturday in the cities of Mier, Camargo and Miguel Alemán.

The Mexican government's role in combating the violence remained unclear. The army presence in some cities appeared sporadic, and the navy has led operations including the December takeout of kingpin Arturo Beltran Leyva in Mexico City.

Gonzalez, the Zapata sheriff, said he couldn't confirm reports that the helicopter was scoping the home of a drug criminal. He said the incursion about a mile over the border occurred over a neighborhood populated by many U.S. Customs officers who work at area border crossings — and they knew what they were seeing.

“My understanding is the U.S. military were informed,” he said. “I don't know what action was taken, if any.”