NEEDLES, Calif. (AP) — There may finally be a breakthrough in a long-running investigation into the killing of wild burros in California’s Mojave Desert nearly five years ago, federal authorities said Thursday.

Nineteen burros were found shot to death along a 50-mile (80-kilometer) stretch of Interstate 15 northeast of Los Angeles on Aug. 13, 2019.

Wild burros are protected under federal law. They are also an iconic symbol of the American Southwest, dating to their days as pack animals for people flocking to California during the Gold Rush.

The Bureau of Land Management said its investigators want to talk to the owners of two vehicles of interest: a gray or silver 2008 Toyota extended cab pickup with flared fenders and a white 2008 Toyota extended cab pickup with a white camper shell and white rims.

Both pickups were recorded on video traveling together that stretch of the highway the day of the killings and were last seen in the parking lot of Whiskey Pete’s Hotel and Casino in Primm, Nevada, the agency said in a statement.

In addition, investigators identified the weapon used to kill the burros as a .30-06 caliber rifle, “possibly vintage based on the rifling of the projectiles recovered, that could have been manufactured by Browning, Remington, Springfield, U.S. Military Arms, or Winchester,” the statement said.

“Special agents also believe the person or persons responsible used reloaded ammunition marked with red/orange paint on the bottom of their cartridges,” according to the bureau.

A $10,000 reward was offered and officials asked anyone with information on possible suspects to contact the bureau.