The Starr County Sheriff’s Office is conducting a criminal investigation into a helicopter crash that killed two National Guard members and a Border Patrol agent, and hospitalized one other person, ABC News reports.

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

The March 8 crash involved a National Guard helicopter in La Grulla that killed U.S. Border Patrol agent Chris Luna of Edinburg, and Chief Warrant Officer 2 Casey Frankoski and Chief Warrant Officer 2 John Grassia. The officers were members of the New York Army National Guard.

ORIGINAL STORY: 3 dead, 1 injured in helicopter crash near La Grulla, investigation underway

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, according to ABC News.

According to ABC News, 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 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," Starr County Sheriff's Office spokesman Major Carlos Delgado told ABC News by email.

RELATED STORY: Fallen Border Patrol Agent Christopher Luna laid to rest in Edinburg

The cause of the incident has not yet been released.

The local investigation is being conducted independently from the previously disclosed safety investigation that is being led by the Alabama-based U.S. Army Combat Readiness Center.

A fourth person, National Guardsman aircraft crew chief Jacob Pratt, survived the crash. He was hospitalized in McAllen and transferred to the Brooke Army Medical Center in San Antonio.