DES MOINES, Iowa — An Oklahoma woman whose body was found in the back of a semitrailer in Chariton was pinned inside the trailer as it was being loaded with lettuce in Yuma, a medical examiner said Wednesday.

Dr. John Kraemer, director of forensics for the Iowa Medical Examiner's Office, said an autopsy indicates that Sheila Kay Ross, 47, of McLoud, Okla., died as a result of an accident.

"Preliminary autopsy results indicate the cause of death to be due to compressional asphyxiation and at this point in the investigation, her death appears to be accidental," Kraemer said.

The woman's body was found Tuesday in the back of a semitrailer delivering lettuce to a Hy-Vee grocery store distribution center in Chariton.

Ross was reported missing Saturday by her husband, said Officer Clint Norred, a police spokesman in Yuma.

He said the Rosses arrived in their semi to pick up a load from a Dole plant in Yuma about 9:30 p.m. Saturday. Sheila Ross got out of the truck to get some paperwork but never returned, Norred said.

"After a while, Mr. Ross called us and the Yuma police searched the area and couldn't locate Mrs. Ross," Norred said.

Norred said the Rosses owned their own truck. Sheila Ross' body was found in the back of another truck. He said the truck was owned by an R&J Trucking, but he did not know where the company was based. It was previously reported that the company was based in Youngstown, Ohio, but company officials there said they did not own the truck.

Norred said police do not know how Ross ended up in the truck.