COPENHAGEN -- The Danish inventor accused of torturing and killing Swedish journalist Kim Wall during a private submarine trip before dismembering her body strongly denied killing her, asserting at his trial Thursday that she died accidentally because of a pressure problem in the submarine.

Peter Madsen, who is accused of torturing Wall before he either cut her throat or strangled her on his submarine, also denied he was sexually attracted to her.

Sitting on his hands as he testified at the opening of his trial in Copenhagen City Court, Madsen appeared irritated at times as he brushed off any suggestion of sexual activity with Wall before or after her death.

Prosecutor Jakob Buch-Jepsen read from a psychiatric report describing Madsen as an intelligent man "with psychopathic tendencies." Madsen himself told the court Thursday that he was "a promiscuous person."

Madsen has admitted to dismembering Wall's body before he "buried her at sea," saying he could not lift her up the submarine tower in one piece to throw her overboard so he had to cut her up.

Wall, a 30-year-old freelance journalist who wrote for The New York Times, The Guardian and other publications, embarked on Madsen's submarine on Aug. 10 to interview the 47-year-old co-founder of a company that develops and builds manned spacecraft. Her remains were found in plastic bags on the Baltic Sea bed weeks later, and her torso was found stabbed multiple times.

Buch-Jepsen started the 12-day trial by reading out the charges, describing in detail how Wall's body parts were found on the ocean bed. He said Madsen has "no empathy or feelings of guilt," citing the court-ordered psychiatric evaluation.

If found guilty, Madsen faces between five years and life in prison -- which in this case means 16 years that could be extended as long as Madsen is deemed dangerous -- or he could be locked up in a secure mental facility if deemed necessary by psychiatrists, for as long as he's considered sick and a danger to others.

Madsen, wearing glasses, a dark shirt and jeans, listened quietly with his fists closed. Wall's parents were also present Thursday at the trial.

Testifying, Madsen repeated his claim that Wall died accidentally inside the UC3 Nautilus while he was on deck. He said Wall "had a wonderful evening until it ended in an accident."

Madsen had offered shifting explanations for Wall's death prior to the trial. He initially told authorities he had dropped Wall off on a Copenhagen island several hours into their submarine trip. Then he said that Wall died accidentally inside the submarine when a hatch fell and hit her on the head.

On Thursday, he described how he found Wall lifeless after a sudden pressure problem in the submarine.

"I could not open the hatches. I heard Kim, it was not good," he said. He added that he tried to give her first aid when he finally reached her, but stopped because it was impossible to stay inside. "There was a risk of having a submarine with two deaths," he told the court.

The prosecution claims Wall's murder was premeditated because Madsen brought along tools he normally didn't take when sailing.

Buch-Jepsen said the cause of Wall's death has not yet been established. He said Wall's blood was found on Madsen's nose and his bodysuit, and that detectives found violent videos and texts about killing women on Madsen's laptop and an external hard drive.

Members of the court were shown a drawing of the multiple stab wounds to Wall's torso. An audio file of a radio exchange between Madsen and maritime officials on Aug. 11 -- the day after Madsen and Wall embarked on their submarine trip-- was also played. In the recording, Madsen said he had let Wall on an island, and that there were no injured persons aboard but only technical problems.

The 33-ton, nearly 18-meter-long submarine sank south of Copenhagen shortly after being spotted afloat. Madsen reported "man overboard" over the radio and was then picked up alone.

Wall, who had previously reported on topics including tourism in post-earthquake Haiti, studied at Paris' Sorbonne university, the London School of Economics and Columbia University in New York.

Caterina Clerici, a friend from Columbia, said Wall had "a soft spot for misfits, for places and people that did not conform."

Madsen was a co-founder of Copenhagen Suborbitals, a private aerospace consortium that developed and constructed manned spacecraft. In 2011, it launched a 30-foot (nine-meter) rocket five miles (eight kilometres) into the sky over the Baltic Sea, a step toward its unrealized goal of launching a person into space.

In an interview with Danish weekly Soendagsavisen in 2014, Madsen said he one day "hoped to have a criminal career," adding he didn't want to rob a bank because "no one must be hurt."

Police believe Madsen sank the submarine on purpose, and later found videos of women being tortured and killed on his personal computer in his hangar. He did not make the videos himself, investigators said.

The next court session is scheduled for March 21. The trial ends April. 25. A verdict is expected that day.