Texas sheriff conducting criminal investigation into deadly National Guard helicopter crash near border

A deadly crash involving a National Guard helicopter is the focus of an investigation in Texas into whether there was any criminal wrongdoing involved, ABC News has learned.

The March 8 incident near the U.S.-Mexico border resulted in the deaths of Chief Warrant Officer 2 Casey Frankoski and Chief Warrant Officer 2 John Grassia, who were members of the New York Army National Guard, and U.S. Border Patrol agent Chris Luna, a South Texas resident, U.S. officials said.

An unidentified National Guard member was injured in the collision, which occurred in rural Starr County.

Although the crash involved a New York-based crew, the UH-72 Lakota helicopter was assigned to Washington, D.C.’s Army National Guard, according to military officials.

The cause of the crash has not yet been released.

"The case has been turned over to the Department of Defense, however, we still are doing our own investigation to determine whether or not any type of criminal activity may have occurred," Major Carlos Delgado of the Starr County Sheriff's Office told ABC News by email.

Delgado later noted that "the official investigation started immediately after a call was placed to our office requesting emergency medical services and our presence.”

The existence of this investigation was disclosed after ABC News requested a number of public records pertaining to the crash from officials in Starr County under the Texas Public Information Act.

The Office of the Starr County Attorney and the Starr County Sheriff’s Office initially referred ABC News’ request to the Department of Defense. When ABC News clarified it was seeking records held at the local level, the county denied the request, citing a Texas law that says that the “release of the information would interfere with the detection, investigation, or prosecution of crime.”

The Starr County criminal investigation is being conducted independently from the previously disclosed safety investigation that is being led by the U.S. Army Combat Readiness Center at Fort Novosel in Alabama.

"Our investigation is only a safety investigation and is still ongoing," U.S. Army Combat Readiness Center spokesperson Jimmie E. Cummings, Jr. told ABC News. "That is the only investigation that we are a part of."

Delgado said that final reports have not yet been delivered to the Starr County Sheriff's Office and that they maintain that Texas law allows them to decline to release additional information.

ABC News’ Luis Martinez contributed to this report.