A multi-agency undercover drug bust in Texas spun out of control Monday afternoon when a civilian working for law enforcement was killed and a police officer injured in what has been described by the local press as a “Mexico-style” attack.

The incident occurred in Texas' Harris County, where parts of Houston are located, when the secret operative disguised as a truck driver delivering a 300 pound package of marijuana was driving through the northwest part of the county to a rendezvous point. Out of nowhere three sport-utility vehicles carrying alleged Zetas drug cartel gunmen cut off the 18-wheeler truck and opened fire on the cab, killing the driver.

"We are not going to tolerate these types of thugs out there using their weapons like the Wild, Wild West," Javier Peña, the new head of the U.S. Drug Enforcement Administration's Houston Division, told the Houston Chronicle. "We are going after them."

As the gunmen opened fire on the truck,  law enforcement officials descended on the scene in an effort to apprehend the shooters. "Officers engaged in gunfire with the suspects. That exchange resulted in the undercover officer being shot in the leg and the death of the occupant in the 18-wheeler," a press release from Harris County Sheriffs Office stated.  

So far four suspects, all believed to be Mexican, have been arrested and charged with murder.

While the men - Eric De Luna, 23; Fernando Tavera, 19; Ricardo Ramírez, 35 and Rolando Resendiz, 34 – have all allegedly admitted to an affiliation with the violent Mexico-based Zetas cartel, U.S. authorities are still puzzled as to why the group would authorize such a brazen attack on U.S. soil for 300 pounds of marijuana.

"If it was a straight assassination, there were points in this controlled delivery where he would have just been a sitting duck," a law-enforcement source speaking on the condition of anonymity told the Chronicle. "Pretty brazen to kill a man over 300 pounds of grass.”

The Zetas are one of the most violent and powerful cartels operating in Mexico today. The former paramilitary-wing of the Gulf cartel is considered to be one of two dominant cartels in Mexico, along with Joaquín “El Chapo” Guzmán's Sinaloa cartel. 

The group is believed to be responsible for the attack on a casino in Monterrey earlier this year that left 52 people dead. 

The sheriff’s deputy who was hit in the knee with a bullet during the attack is expected to be in the hospital through Thursday night, but will make a full recovery. Authorities are keeping quiet about who shot the sheriff’s deputy as the incident is still under investigation.

They also did not release any information about the driver who was killed.

"Everybody is surprised at the brazenness," Peña said, according to the Chronicle. "We haven't seen this type of violence, which concerns us."

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