COPENHAGEN — Peter Madsen, a Danish amateur space rocket and submarine builder, has admitted during an interrogation that he mutilated the body of the Swedish journalist Kim Wall, the police in Copenhagen said on Monday.

While he confessed during questioning on Saturday to tossing her body parts into Koge Bay, Mr. Madsen again denied killing her, saying that she had died on Aug. 10 from carbon monoxide poisoning inside his submarine while he was on its deck, the police news release said.

It was yet another account from Mr. Madsen, 46, who is being held in Vestre Prison charged with manslaughter, which in Danish law is the equivalent of murder. Previously he said that Ms. Wall had left his vessel alive, then that she had died after being accidentally hit in the head by a 150-pound hatch door.

The chief police investigator, Jens Moller Jensen, said Mr. Madsen did not say why he had dismembered Ms. Wall, who disappeared after meeting the inventor for an interview. Her torso was found on Amager Island, near Copenhagen, 11 days later.