Danish submarine inventor Peter Madsen, convicted of torturing and murdering Swedish journalist Kim Wall aboard one of his own vessels last year, lost his appeal Wednesday against his life sentence.

The Danish version of a life sentence typically is about 16 years long, but it may be continuously extended if the court rules that circumstances call for it. Madsen had sought a time-limited term. Now the 47-year-old could potentially spend the rest of his life in prison.

His defense had argued that Wall’s death was an accident, although Madsen himself admitted to throwing her body parts into the Baltic Sea.

The prosecution had argued that Madsen’s motive was sexual and that the murder was planned.

“I’m terribly sorry to Kim’s relatives for what happened,” Madsen told the court. Wall’s parents were not present.

A Copenhagen court ruled in April that Madsen had lured Kim onto his home-made submarine UC3 Nautilus with the promise of an interview, where she then died. The exact cause of her death has never been established.