COPENHAGEN (REUTERS) - Danish police are putting an additional charge of abuse of a corpse to the court investigating whether Danish inventor Peter Madsen killed Swedish reporter Kim Wall on board his submarine.

Police said on Wednesday, as they formally identified her headless torso, that the body had been weighted down with metal and an attempt had been made to remove gas and air from inside it to keep it on the seabed.

Wall, who was researching a story on inventor Peter Madsen, went missing after he took her out to sea in his 17m submarine on Aug 10. He denies killing her, saying she died in an accident.

Police charged Madsen with manslaughter, which carries a sentence of between five years and life in prison, on Aug 11 when he was rescued after his submarine sank.

Police spokesman Jakob Buch-Jepsen said the prosecutor was also adding a charge of abuse of a corpse.

In its preliminary investigation, the court ordered Madsen detained until Sept 5, pending further inquires, on the lesser charge of involuntary manslaughter.

Police will seek to extend the pre-trial custody when it is reviewed next month, again requesting he be held on the charge on manslaughter, Buch-Jepsen said.

"We maintain the (manslaughter) charge that we've had all the time, but now we would like the court to change the basis for the custody to manslaughter from involuntary manslaughter," he said.

Under the Danish penal code, manslaughter is used to describe the deliberate killing of a person and there is no distinction between manslaughter and murder. Involuntary manslaughter is used when the killing is not intentional.

The submarine is one of three constructed by Madsen and one of the largest privately built ones in the world. It can carry eight people and weighs 40 tonnes when fully equipped.

Police still do not know the cause of Wall's death, and divers are searching for more body parts.