The reward offered over the roadside shooting of two horses at a well known American arabian stud has reached $US10,000.
The reward has doubled as efforts continue to find those responsible for the death of Sweet Sanadika V, who was 20, and the serious injury of 26-year-old Mosquerade V.
The shootings occurred at Varian Arabians in rural Arroyo Grande, about an hour north of Santa Barbara in California.
Staff heard multiple gun shots from the nearby roadway at around 8.30pm on December 30. Staff checking the pasture along Corbett Canyon Rd shortly after 7am the next day discovered the two shot mares.
Sweet Sanadika V had to be euthanized by a veterinarian.
The San Luis Obispo Sheriff's Department is seeking public help in finding those responsible for attack.
San Luis Obispo County Crime Stoppers said the reward is one of the largest rewards in an animal cruelty case ever offered by the Crime Stoppers programme.
There are no suspects in the case.