Just a few hours before embarking on his fateful submarine trip with Swedish journalist Kim Wall, Peter Madsen worried that he lacked the self-control to face a murder trial.

“He talked about how he needed to learn to shut up because he had difficulty keeping things to himself,” Australian documentary maker Emma Sullivan told the Copenhagen district court last month, referring to an interview she filmed that summer afternoon with the Danish rocket and submarine builder.

If he were, for instance, to become the main suspect for the murder of his neighbour’s wife, he speculated he would find it hard to keep quiet, even though he knew he was entitled not to comment, and that anything he said was likely to be used against him.

When Danish prosecutor Jakob Buch-Jepsen sums up the first 10 days of Madsen’s trial for murdering Wall on Monday, the 47-year-old is likely to discover how right he was in that self-assessment. The first thing he said in court when the trial began at the start of last month, after denying that he murdered Wall, appeared to reveal the “narcissistic traits” forensic psychiatrists had identified.

“There is nothing worse that can happen to a person like me,” he said of the gruesome death and dismemberment of the talented 30-year-old journalist. “The moment Kim Wall died, there was nothing left for me to fight for.”

The case has gripped Denmark and Sweden, with at least six newspapers and broadcasters live-blogging every minute of the trial. “Everyone follows it,” says Anna Gottschalk, who covered the trial most days for the Berlingske newspaper. “It doesn’t matter if you’re at a café or a family birthday, everyone knows this case.”

The interest has also been international. The court had to open a special room with a video link to accommodate more than 115 journalists from 15 countries, drawn by the unusual suspect, with his rocket-building projects, and the macabre circumstances of Wall’s death on his submarine.

Buch-Jepsen believes Madsen strangled or beheaded Wall after torturing her to fulfil a violent sexual fantasy. The prosecutor read out and played a selection of more than 140 clips or links showing murder, torture, beheading and the sexual torture of women that were found by police on Madsen’s computer, hard drives and among the reconstructed contents of his iPhone. The night before Wall’s death, he Googled “beheading” and “girl”, and then watched a video of a girl having her throat slit.

But when Madsen gave his own account of how Wall died from asphyxiation after an accident caused the submarine to fill with exhaust fumes, he was so plausible that it was easy to see how he had convinced so many people that he could launch a manned space mission from a rusty hangar in a disused Copenhagen shipyard.

When Buch-Jepsen read part of a text found on one of Madsen’s hard drives about torturing women with skewers, the defendant maintained it was no different from a horror film. “Of course it’s crazy,” Madsen said, ignoring the chilling parallels between the content and the wounds on Wall’s body. “It’s as crazy as the movie you’ve seen, Seven. It’s the same as films you’ve seen, Jakob.”

Cross-examined on how and why he cut off Wall’s arms, legs and head, Madsen initially appeared subdued, calling it “a very, very traumatic event, which I do not want to describe”. Eventually he admitted he had no idea why it had been necessary to cut off Wall’s head to remove her body from the submarine.

Kim Winther, an expert witness from the Danish Technological Institute, had told the court that Madsen’s account of the accident was technically “plausible”, and questioned the claim made by a submarine expert that traces of carbon monoxide or soot would necessarily have been found in the submarine and its filters if his account was true.

The fact that forensic pathologists have been unable to determine the exact time or cause of Wall’s death could also be a problem for the prosecution. However, Mette Grith Stage, who has defended some of Denmark’s most high-profile murderers, told the Observer that the defence faced “an uphill struggle”. “It doesn’t make it any easier when he has all this material on his computer,” she said.

The forensic pathologist found no signs of carbon monoxide poisoning on Wall’s body, and determined that some of her wounds were inflicted when she was alive, or very shortly after death, rather than many hours later, as Madsen claims.

The biggest problem for the defence, Stage said, was Madsen’s own shifting testimony, which has moved from a claim that he dropped Wall on land alive, to saying that she died when a heavy hatch fell on her head, to saying she died of asphyxiation. “In a case like this where you don’t have any witnesses, it’s very important that the defendant is trustworthy, and he was in the beginning,” Stage said. “But every time the police came up with something new, he had to make a new explanation, and this has happened so many times that he’s not trustworthy any more.”

The verdict is due on Wednesday.