(Reuters) - An investigation of Danish inventor Peter Madsen’s homemade submarine showed no traces of exhaust gases, a witness told a Copenhagen court on Tuesday, casting doubt on Madsen’s explanation that Swedish journalist Kim Wall died last August after breathing exhaust fumes.

“We have not been able to detect Co2 in the submarine,” Ditte Dyreborg, a lieutenant commander in the Danish Navy, told the court, according to Danish broadcaster DR. “And the experience from military submarines is that it wouldn’t pose a significant risk.”

Madsen, 47, is accused of murdering and dismembering Wall, a 30-year-old Swedish journalist who was researching a story on the Danish inventor and the submarine he had built. Prosecutors say she died either by strangulation or by having her throat cut. Madsen faces up to life in prison if convicted .

He denies murdering Wall, although he admits he cut up her body so he could get it out of the 17-metre (56-foot) submarine. He intended to dispose of the body parts at sea to restore a “normal” condition on board, he said, adding that he was not thinking rationally at the time.