SAC CITY, Iowa (AP) — An Iowa truck driver who vanished last fall and whose body was found in a farm field this spring died of hypothermia related to acute methamphetamine intoxication, an autopsy found.

State medical examiner Dr. Kelly Kruse ruled that 53-year-old David Schultz’s death was an accident, the Sioux City Journal reported. Schultz, who was also a farmer, was found dead on April 24 in a Sac County field about a quarter-mile (half a kilometer) from where his semi was found parked in the middle of the road on Nov. 21.

Kruse ruled out homicide, noting that Schultz apparently took meth and was then exposed to the cold. She didn’t immediately respond to an Associated Press phone message Friday seeking further information.

In the days after Schultz disappeared, the temperatures fell well below freezing.

Schultz, of Wall Lake, left home late on the night of Nov. 20 to pick up a load of pigs from a hog confinement near Eagle Grove. He was expected to deliver the pigs the next morning to a livestock dealer in Sac City, a small town about 90 miles (145 km) northwest of Des Moines. When he didn’t show up, no one could get him on the phone.

After his wife reported him missing, Schultz’ truck was found that afternoon, less than 10 miles (6 kilometers) northeast of his destination. The pigs were still in the trailer. Schultz’s wallet and phone were inside his rig, but his jacket was on the roadside.

Law enforcement searched the area before more than 250 volunteers joined in a wider effort. But his body wasn’t found until spring.