Danish submarine inventor Peter Madsen, who was found guilty of the torture, sexual assault, murder and dismemberment of a Swedish reporter, has appeared before an appeals court to fight against his life sentence.

The three-day session at the Eastern High Court in Copenhagen will not deal with the April 25 guilty ruling.

Madsen, 47, still denies murdering 30-year-old Kim Wall but has accepted the verdict in order to move on, according to his lawyer.

In Denmark, a life term is on average 16 years, but it can be extended if necessary.

Madsen, who claims Ms Wall died accidentally inside the submarine in August 2017, wants a time-limited sentence, not an open-ended term.

UC3 NautilusThe UC3 Nautilus, where Ms Wall died (AP)

He has confessed to throwing her body parts into the Baltic Sea.

Wearing a dark blazer, a black T-shirt and jeans, Madsen listened quietly as prosecutor Kristian Kirk read out the April verdict to present the case.

He later looked away when Kirk played a police video of the inside of his UC3 Nautilus submarine, which he had claimed was the largest privately built submarine in the world.

The Copenhagen City Court had ruled unanimously that Madsen had lured Ms Wall onto his home-made submarine with the promise of an interview.

Betina Hald EngmarkMadsen’s lawyer Betina Hald Engmark (AP)

The court ruled the murder was sexually motivated and premeditated, with the prosecution using Madsen’s shifting explanations against him and quoting a court-ordered psychiatric report that described him as “emotionally impaired with severe lack of empathy, anger and guilt” and having “psychopathic tendencies”.

Madsen’s lawyer Betina Hald Engmark said the prosecution case was based “on undocumented claims”.

Clearly, she said, Madsen did something “horrible” by cutting Ms Wall into pieces, but she said he should only be sentenced for that, noting that the cause of death has never been established.

Under Danish law, “indecent” handling of a corpse carries a maximum sentence of six months in jail.

Ms Wall wrote for The New York Times, The Guardian and other publications. She had reported from post-earthquake Haiti, among other places, and studied at Paris’ Sorbonne University, the London School of Economics and Columbia University in New York.

She set out on the submarine on a sunny August evening last year to interview Madsen, the co-founder of a company that develops and builds manned spacecraft.

Her remains were found in plastic bags on the sea bed weeks later.

Madsen initially said he had dropped Ms Wall off at a Copenhagen island several hours into their submarine trip.

Then he claimed Ms Wall had died as a result of a build-up in pressure inside the submarine. He later changed this to say that the reporter had died accidentally inside the vessel when a hatch fell and hit her on the head — but there was no indication of a skull injury when Ms Wall’s head was finally located.

A decision is expected on September 14.