A Texas prison warden and his brother face charges in a shooting that killed a migrant and injured another

 (CNN) -- The former warden of a Texas prison and his brother were arrested and now face manslaughter charges in the fatal roadside shooting of a migrant this week.

A migrant woman also suffered a gunshot wound to the stomach in the Tuesday incident, authorities said.

Michael and Mark Sheppard, both 60, were arrested Thursday, according to the El Paso County Sheriff's Office.

The men are accused of pulling their truck over near the town of Sierra Blanca, located off Interstate 10 about 25 miles from the Mexico border, and opening fire on a group of migrants getting water along the road, the Texas Department of Public Safety said in a statement.

The shooting killed a man at the scene. The injured woman was recovering Thursday at a hospital in El Paso.

Immigrant rights advocates said this area of West Texas has become an increasingly busy route for migrants, and to reach the area, migrants have likely been walking for days in harsh conditions.

Asked if Michael Sheppard still worked for LaSalle Corrections, the private prison company said in a statement from spokesperson Scott Sutterfield the warden at West Texas Detention Center in Sierra Blanca had been fired "due to an off-duty incident unrelated to his employment."

Sutterfield declined to provide additional details, citing the criminal investigation.

West Texas Detention Center contracts with US Immigration and Customs Enforcement to hold undocumented migrants.

The brothers remain in custody, according to the sheriff's office. It's unclear if they've obtained legal representation or if bail has been set.

Affidavit: Migrants hid as truck approached

The migrants were traveling through the desert in Hudspeth County on Tuesday evening, right around sunset, and stopped to drink from a reservoir when a truck approached, according to an affidavit signed by a Texas Ranger.

"The group took cover to avoid being detected. The vehicle then backed up and the driver exited the vehicle. The driver leaned on the hood of the vehicle and fired two shots from a firearm at the group. ... The driver then re-entered the vehicle and fled the scene," the affidavit said.

The migrants told authorities they heard one of the men hurl profanities in Spanish and rev the truck, it said, and as they looked up from the brush where they were hiding they heard two gunshots.

Agents checked cameras and found a vehicle that matched the migrants' description. They later found the truck at Michael Sheppard's home in Sierra Blanca, where Sheppard acknowledged the truck belonged to him, the affidavit said.

Sheppard was "reluctant to speak" and left, the Ranger's affidavit said, and authorities then conducted an interview with his brother, who first said he hadn't been in the location of the shooting before conceding he and his brother had been near the reservoir looking for game, it said.

Mark Sheppard "said they were looking for ducks, then changed it to birds" and then to javelinas, a type of wild pig, the affidavit states. Mark Sheppard saw a "black butt" he thought belonged to a javelina, he said, according to the affidavit.

That's when his brother "exited the truck with a shotgun, leaned on the hood of the vehicle and fired two rounds," and Mark asked his sibling if he'd hit anything, the affidavit said.

"I asked (Mark Sheppard) if either he or his brother went to confirm that they had shot anything, and he said they did not. Mark Sheppard told us they never yelled anything and after shooting then left to attend a Hudspeth Water Board meeting," the Ranger wrote in his report. "Mark Sheppard told us this was when he heard on the radio that an illegal immigrant was found at the dump suffering from a gunshot wound. Mark Sheppard told us Michael Sheppard stated that's too far from where we were shooting."

When asked what he did upon learning a migrant had been found dead at the location where his brother was shooting, Mark Sheppard said they'd done nothing and hadn't contacted law enforcement, the affidavit said.

Sierra Blanca is about 90 miles southeast of El Paso.

Texas Rangers are leading the investigation, with the assistance of the FBI, US Border Patrol and the Department of Homeland Security.

"As this is an active and ongoing investigation by the Texas Rangers, no additional information is available at this time," the state Department of Public Safety said in the statement.

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