Betty Rowbotham told a Winnipeg murder trial that she saw a stain on the garage wall where police believe her sister was slain.

Rowbotham told court on Thursday the wall was clean before her sister, Beverly, died. She noticed the stain a few days later, she told jurors at the second-degree murder trial of Beverly's husband, Mark Stobbe.

Beverly Rowbotham was found dead in her car at a gas station near Selkirk, Man.

Rowbotham also told court she didn't remember seeing a large stain on the garage floor prior to her sister's death. The stain is visible in a police photograph taken afterwards.

Stobbe, who worked as a senior adviser to former Saskatchewan premier Roy Romanow before moving to Manitoba for a job with the provincial government, is accused of killing his wife in October 2000.

He has pleaded not guilty.

Mark Stobbe is charged with second-degree murder in the death of his wife, Beverly Rowbotham. (CBC)

The Crown alleges Stobbe killed Bevery during a heated argument in the family's backyard by hitting her in the head 16 times with a hatchet.

The Crown's theory is that Stobbe then dragged his wife to one of the family's two cars in the garage, drove to Selkirk, Man., then bicycled back home and reported her missing hours later.

Beverly was found dead in her car at a gas station near Selkirk, Man. Two of her fingers and part of her skull were chopped off, Crown prosecutor Wendy Dawson has said.

During cross-examination on Wednesday of an RCMP forensics expert, Stobbe's defence lawyer Tim Killeen appeared to suggest some of that material could have been related to a tree stump the family used as a block to chop wood.

The trial is scheduled to run until the end of March.

The Crown's case is largely circumstantial as there were no witnesses to Beverly's death and no murder weapon was ever recovered.