COPENHAGEN, DENMARK -- The Danish inventor sentenced to life in prison for the murder of journalist Kim Wall aboard his homemade submarine has admitted to the crime for the first time in a documentary broadcast Wednesday.

The admission from Peter Madsen comes three years after Wall's death, which drew massive worldwide attention.

The 49-year-old engineer, who was interviewed over the phone, answered "yes" when a journalist asked him if he killed the 30-year-old woman who was interviewing him in August 2017.

"There is only one who is guilty, and that is me," Madsen said in the documentary.

During his trial, Madsen had insisted that Wall's death was an accident on his submarine, but admitted to chopping up her corpse and throwing her body parts into the sea.

Wall, an award-winning reporter, had boarded the submarine to interview the eccentric self-taught inventor for a profile she was writing about him.

"Apart from August 10, 2017, I've never done anything to anyone," Madsen said in the documentary series entitled "Secret Recordings with Peter Madsen".

Madsen changed his version of events several times after his arrest and throughout his trial, but ultimately testified that Wall died when the air pressure suddenly dropped and toxic fumes filled his vessel while he was up on deck.

'PATHOLOGICAL LIAR'

In the documentary, Madsen said he and Wall had a discussion that "shook things up", and that's what caused him to kill her.

Yet at the same time, he also said she touched a landmine, which exploded and killed her.

"Here he's trying to put the blame on Kim Wall, and it's a classic characteristic for murderers like Peter Madsen with psychopathic traits," former police investor Kurt Kragh told tabloid Ekstra Bladet.

"They never take reponsibility for their actions, regardless of how serious they are. He's trying to justify what he's done."

An autopsy report presented at length during the trial concluded that Wall probably died from suffocation or having her throat slit, but the decomposed state of her body meant examiners could not determine the exact cause of death.

There was no mention of injuries consistent with an explosion.

Fourteen stab wounds and piercings were however found in and around her genital area.

Madsen had told the court he stabbed her because he wanted to prevent gases from building up inside her torso that would prevent it from sinking to the seabed.

Psychiatric experts who evaluated Madsen for the court found him to be "a pathological liar" who poses "a danger to others" and who was likely to be a repeat offender.

Madsen was convicted of murder and sexual assault in April 2018.

The documentary series is based on more than 20 hours of phone calls recorded between a journalist and Madsen without his knowledge.

Madsen later authorised the journalist to use the recordings for the documentary.

Only the first episode has aired so far.

Another television series currently under production is to examine the complexities of the investigation. Madsen will not participate in that series.