Police said on Wednesday that while there were no major developments in the case, they were continuing to commit undiminished resources to the search for the girl, who disappeared near her home in Østensjø ten days ago.
Witness psychologist Asbjørn Rachlew, who also assisted the police in the questioning of confessed mass killer Anders Behring Breivik, is expected to help police appraise the relative merits of the 1,700 tips they have so far received in the case.
“Sigrid’s parents are obviously very grateful for any positive resources the police commit to the case,” the family’s lawyer Harald Stabell told newspaper VG.
On Tuesday, police said they were seeking to get in touch with the owner of a dark red car observed near the spot where the teenager disappeared at around midnight last Saturday.
“A car was seen in the vicinity of Låveveien at that time, which is to say between midnight and 12.30am. It was a passenger car; we don’t know the model or make, but it has been described as burgundy, wine red, or dark red,” said police investigator Grete Lien Metlid.
Sigrid Giskegjerdet Schjetne was reported missing by her parents at 12.30am on Sunday, when she failed to arrive home after having been at a friend's house two kilometres away.
Police found the girl's shoes, mobile telephone and a sock near the teenager's home.
She is reported to have had contact with friends via SMS while walking home and none reported any behaviour deemed out of the ordinary.
Local resident Anne-Mette Jørgensen Saethre reported hearing a scream at around 12.30am near a children's daycare centre, only 300 metres from the teenager's home.
"We heard a long, frenetic and scared scream... My daughter said it sounded like a painful cry," she told NTB.
The teenager was wearing jeans shorts, a blue jumper and a grey singlet when she disappeared. She is 16-years-old, 170 centimetres tall and has light brown hair and blue eyes.
Police have called for anyone who was in the vicinity of Skøyenåsen between 11.30pm and 1am to get in contact by calling 02800.
Close friends of the girl are continuing to coordinate daily searches in the area.