A leading submarine expert on Tuesday challenged Danish inventor Peter Madsen's claim that Swedish journalist Kim Wall was killed by toxic fumes in his homemade vessel last year, as he faces trial for her murder. 

Madsen, 47, who is accused of premeditated murder, sexual assault and desecration of a corpse, has said her death was accidental since the first day of his trial on March 8.
He said Wall, 30, died when a hatch fell on her head, but later changed his story after autopsy concluded there had been no damage to the skull. 
Madsen has admitted dismembering her body and throwing it overboard, but denies premeditated murder and sexual assault.
The self-taught engineer said the freelance journalist died when the air pressure suddenly dropped and toxic fumes filled his vessel on the night of August 10, 2017, while he was up on deck.
Ditte Dyreborg, a prominent lieutenant commander known for having a sex change operation to become a woman at the end of an impressive career in the Royal Danish Navy, said Madsen's explanations were implausible, if not impossible, as she spoke in a Copenhagen court on Tuesday. 
"We did not find anything. No CO (carbon monoxide), no CO2 (carbon dioxide), no NOx (nitrogen oxide). Which we would have if the submarine engine was running with carbon monoxide in it," said Dyreborg, who was the first to inspect the vessel on August 11. 
Seemingly irritated and agitated, Madsen took notes during Dyreborg's testimony and whispered technical questions into his lawyer's ear, according to an AFP reporter at the scene. 

 'Perverse polymorph' 

A coroner told a March 22 hearing that there was no conclusive evidence to prove Wall's cause of death beyond doubt, adding she was probably strangled or had her throat cut. 
The coroner could however not rule out poisoning as a result of toxic fumes.
Madsen's lawyer Betina Hald Engmark questioned the relevance of Dyreborg's expertise on smaller and private submarines, concluding the lieutenant commander did not carry out any tests on the vessel's air filters. 
The prosecution, which is seeking a life sentence for Madsen, claims he tortured and killed Wall as part of a sexual fantasy. 
Wall's body parts, weighed down with metal objects, were recovered from waters off Copenhagen. She also had 14 stab wounds to her genital area. 
The first hearings focused on the inner workings of the eccentric inventor described by psychiatric experts as a "perverse polymorph" with "psychopathic traits". 
The verdict is expected on April 25.