Testifying in court on Tuesday, Madsen claimed he had been holding the hatch for Ms Wall and had slipped, causing the heavy cover to fall on the journalist.
“I lose my foothold and the hatch shuts,” he said. “Kim had been severely hurt and was laying with an intense bleeding. There was a pool of blood where she had landed.”
The accident happened as the pair were sailing in the strait between Denmark and Sweden, he claimed.
Ms Wall, a Swedish freelance reporter, had been visiting Madsen in his Nautilus submarine to research an article when she disappeared on the night of 10 August.
Private ships and the Danish navy were called to an emergency search for the 60ft submarine after Ms Wall was last seen boarding it and did not return home.
The following morning Madsen had to be rescued from the vessel as it sank, initially telling authorities that Ms Wall had been safely dropped off near Copenhagen.
But when it emerged the reporter was still unaccounted for he told investigators she had died in an accident on board. He was then charged with manslaughter.
Ms Wall’s mutilated remains – a torso with the head, arms and legs sawn off – were later discovered by a cyclist in Koge bay.
Investigators later revealed that the body, identified by DNA evidence, had been attached to a piece of metal and cut in a way that aimed to ensure it would sink and remain on the sea bed. The rest of Ms Wall’s remains have not been found.
Police also concluded that the submarine – built and crowdfunded by Madsen himself, and the largest privately built vessel of its kind – had been purposefully sunk.
Strict reporting restrictions in Danish courts mean only limited information has been available on the case and the cause of the young woman’s death has not yet been determined.
Ms Wall, 30, was a respected freelance journalist, who had reported from China, Uganda and Haiti for a wide range of publications, on topics including furries, feminism and voodoo.
Commenting on her death, her family said her work had brought her to many dangerous places, but that it was “unimaginable” something could happen “just a few miles from the childhood home”.