Updated

A grand jury on Tuesday declined to indict a Texas trooper who fired from a helicopter on a fleeing pickup truck along the U.S.-Mexico border, killing two Guatemalan immigrants.

Prosecutors in Hidalgo County presented the case to a grand jury to investigate and determine whether to indict Trooper Miguel Avila of the Texas Department of Public Safety in the October 2012 incident.

The DPS has said Avila was aboard the helicopter and believed drugs were in the truck's bed when he opened fire during the pursuit near La Joya. The trooper opened fire to disable the vehicle because it was barreling toward a school zone, the DPS has said.

Instead, nine Guatemalans and a teenage driver were found by authorities on the ground. Six of the Guatemalan immigrants were under a sheet, two of them wounded fatally.

Nevertheless, DPS revised its policies in February to prohibit shooting from the sky unless the aircraft is fired upon. According to the revised policy, "a firearms discharge from an aircraft is authorized only when an officer reasonably believes that the suspect has used or is about to use deadly force by use of a deadly weapon against the air crew, ground officers or innocent third parties."

A suspect driving aggressively or recklessly does not constitute use of a deadly weapon, the new policy states.

The incident began with a chase after Texas Parks and Wildlife game wardens spotted a red pickup near La Joya, about 250 miles south of San Antonio. The wardens requested help, and the DPS helicopter joined midway in the 14-mile, high-speed pursuit of what authorities said they believed was a "typical covered drug load."

In the days following the incident, civil rights groups and the Guatemalan government expressed concerns that DPS essentially was investigating itself because the Texas Rangers, who were leading the investigation, fall under the DPS umbrella.

Hildago County's district attorney said he would take the case to a grand jury, which is an investigative body. While the district attorney guides grand juries in their efforts and presents evidence, they can take the investigation in any direction they see fit.

A messages sent to the Guatemalan consulate was not returned Tuesday.

A DPS statement expressed appreciation for the work of "all involved throughout this case, including Hidalgo County District Attorney Rene Guerra and the Hidalgo County grand jury."

The teenage driver, now 15, was arrested, released by mistake, arrested again in December driving a stolen vehicle and placed on probation to be deported. He was arrested again last month by the U.S. Border Patrol.