Police are testing the truth behind claims by a man that he ran over missing Melbourne schoolgirl Siriyakorn "Bung" Siriboon by mistake and dumped her body in a reserve.
Chief Commissioner Ken Lay says police are checking the story and comparing it with forensic evidence.
The 13-year-old vanished on her way to school after leaving her home in Boronia in June 2011.
A 24-year-old man has twice been arrested - first in August and then in October - and questioned over Bung's disappearance but both times has been released without charge.
Mr Lay said police have a number of persons of interest, including the man.
"We have spoken to one particular person on two occasions. We are now testing the veracity of the story with forensic evidence," Mr Lay told Fairfax Radio on Wednesday.
"We need to double check it to ensure it adds up."
The man claims he hit and killed the high school student while driving his car on the morning she disappeared, then panicked and disposed of her body at a local reserve, the ABC reported.
Police conducted a five-day search of Old Joes Creek Retarding Basin in Boronia in October but did not find any human remains.
"We've done that search and unfortunately we couldn't find anything although we are still doing some testing on some articles that may well put us in a different place in the near future," Mr Lay said.
Some forensic testing had been done on a car that may be related to her disappearance.
Mr Lay said the investigation was moving, but police have little hope of finding Bung alive.
"People are holding out hope, we are fearing the worst," he said.
Taskforce Puma shut down in October this year and the case returned to the Homicide Squad, but police said they had not given up on finding the missing girl.
