COPENHAGEN — The Danish inventor Peter Madsen was formally indicted on Tuesday on charges of homicide in connection with the death in August of Kim Wall, a Swedish journalist who had boarded his submarine to interview him.

Danish prosecutors and the Copenhagen police indicted Mr. Madsen on charges of killing Ms. Wall “with prior planning and preparation” — the equivalent of murder — according to a statement released by the police, as well as with dismemberment, indecent handling of a corpse and improper sexual relations. While a news release was posted online on Tuesday, the actual wording of the charges is expected to be made public only next week.

Ms. Wall, a freelance journalist, vanished on Aug. 10 after leaving the port of Copenhagen on the UC3 Nautilus, a submarine that Mr. Madsen had built and operated. Her torso was found on a beach on Amager Island near Copenhagen after 11 days, and divers later recovered her severed head and legs in plastic bags.

Mr. Madsen, 47, has given various explanations for the disappearance of Ms. Wall, 30. But he eventually said that she had died onboard his vessel after a hatch unexpectedly collapsed, and that she had hit her head while she was climbing stairs in the submarine’s tower. An autopsy revealed that she had no head injuries to support that claim, however.

Prosecutors said in the statement on Tuesday that the exact cause of Ms. Wall’s death was not known, but that it “could have taken place by cutting of the throat or strangulation.” An autopsy had found that she had been stabbed at least 14 times, but it was not able to establish the cause of death.

During questioning in October, Mr. Madsen admitted to dismembering Ms. Wall’s body and to tossing body parts overboard, but he denied killing her.

The prosecution said on Tuesday that it would not reveal details on the evidence supporting the charges.

The exact circumstances of Ms. Wall’s introduction to Mr. Madsen remain unclear. In a pretrial hearing in September, he said that she had first contacted him to talk about rockets, but that she had then become intrigued by his submarines and wanted to go on one for a ride. It was not clear when the two first communicated, but they met for the first time on Aug. 10.

Kim WallCreditTom Wall, via Associated Press

Ms. Wall, a prolific journalist who had written for The New York Times, graduated from the London School of Economics, received two master’s degrees from Columbia University and had lived in many countries. She reported from Uganda, Sri Lanka and Cuba, and died only miles from Trelleborg, Sweden, where she grew up, across the Oresund from Copenhagen.

Witnesses have described seeing Ms. Wall and Mr. Madsen onboard the submarine in Copenhagen port on Aug. 10. When she failed to return home that evening, her boyfriend contacted the authorities and the submarine was reported missing.

It was found the next morning floating in Koge Bay, south of Copenhagen, but began sinking when a private rescue party approached. Mr. Madsen was pulled from the waters.

At first, he told the police that he had dropped off Ms. Wall on shore, and denied any wrongdoing. He later said that he had buried her intact body at sea after an accident. When police investigators presented evidence tying him to metal pieces and straps used to wear her body down, he changed his explanation again and admitted to dismembering her.

Betina Hald Engmark, a lawyer for Mr. Madsen, said in a text message Tuesday afternoon that she would review the indictment with her client later on Tuesday, adding that she had no further comment about the charges.

A trial by jury is expected to begin on March 8 and to last eight days. Jakob Buch-Jepsen, a prosecutor, said in a short news briefing on Tuesday that he would seek a life sentence, which he added translates in Denmark to an average of 14 years in prison.

As a routine measure, the Danish Medico-Legal Council performed a psychiatric evaluation of Mr. Madsen, concluding “that safe custody may be required” if he is sentenced.

Ms. Wall’s mother, Ingrid Wall, said on Facebook on Monday that a Kim Wall Memorial Fund had raised $150,000 for scholarships. The first recipient will be announced on March 23, she said.

“In spite of everything, Kim lives on and continues to make a difference,” she wrote.