Investigators are continuing to look into a gruesome accident on U.S. Highway 550 that involved two separate vehicles and killed four horses last week.

The first accident happened around 5 a.m., when 59-year-old David Hollowwa ran into three horses on the highway near mile marker 99, near Cutler Creek. Hollowwa, of Delta, was driving a silver pickup truck to work for a contractor for Ouray Silver Mines, and it was dark.

A white horse was hit so hard on impact that it flipped over the vehicle and l...