The home-made Nautilus submarine where journalist Kim Wall was last seen alive was scanned Tuesday, as authorities hunted for any possible hidden compartments the vessel might contain.
Copenhagen Police, who are still searching for Wall's head and the location and manner of her death, said in a statement a mobile truck scanner typically used to scan shipping containers is being brought in "on the basis of many different inquiries about possible cavities in submarines in general, and specifically also in relation to Nautilus."
The 40-ton, nearly 60 foot-long submarine, which sank earlier this month, now stands on land in a remote corner of Copenhagen's harbor.
As police started the search, a friend of owner and prime suspect Peter Madsen told the Danish BT tabloid it is almost impossible to hide something on board.
Jens Falkenberg, who told the news outlet he was involved in building the vessel, said there is no secret space on board.
"The submarine is not built or prepared to conceal something or have some secret spaces," Falkenberg told the tabloid.
In addition to the search of the sub, police said Swedish colleagues with dogs specially trained to search for corpses in the water were combing the Copenhagen coast looking for clothing and more missing body parts from Wall. That search is expected to last two days, police said.
Wall's naked, headless body was found Aug. 21 on a Copenhagen beach, 10 days after she was last seen entering Madsen's sub.
Police said earlier Wall's head, arms and legs had been deliberately cut off and a piece of metal had been attached to the torso "likely with the purpose to make it sink." Police also said marks on the torso indicated that someone had tried to press air out of the body so it wouldn't float.
A search with a plane over the coastline Monday looking for journalist's clothes, including an orange turtleneck blouse, a black-and-white skirt and white sneakers produced no results, police said.
Madsen, 46, is being held in the death of the 30-year-old Wall, and faces preliminary manslaughter and indecent handling of a corpse charges. He has denied wrongdoing, saying Wall died in an accident, and he buried her at sea.
The inventor was detained after being rescued Aug. 11 from the submarine, which police believe was deliberately sunk.
Last week, Danish Prosecutor Jakob Buch-Jepsen told the B.T. tabloid that police expect to raise the preliminary charges against Madsen to murder and indecent handling of corpse when he appears at a custody hearing Sept. 5 on whether his pre-trial detention should be extended
The Associated Press contributed to this report.