Police hoped the excavation started yesterday would uncover the red Chieftain bicycle being ridden by German backpacker Nancy Grunwaldt when she disappeared on March 12, 1993.

She was last seen four kilometres south of Scamander, riding the bicycle toward Bicheno.

Yesterday Launceston detectives looked on as an excavator prepared to shift 125 cubic metres of rubbish and dirt at the Bicheno Waste Management Centre.

Detective Inspector Scott Flude said police were led to the tip by a Launceston man who had contacted them last year and admitted to having seen the bike 19 years ago.

The tip was not searched at the time.

``This person has been mulling over it for a long period of time, and as a result of newspaper articles in relation to this investigation during the year, they thought it was prudent to come forward and have discussions with us,'' Detective Inspector Flude said.

He said the witness was one of several to come forward after retired detective Bob Coad told The Examiner last year that he believed Miss Grunwaldt had been struck by a car on the Elephant Pass, and that the driver had disposed of the body and other evidence.

Detective Inspector Flude said the witness claimed to have seen the bike ``in a damaged condition'' in a rubbish trench at the tip.

However, he said this should not be taken as positive confirmation of Mr Coad's theory.

``Everyone has got different views on the disappearance of Nancy,'' he said.

``Obviously there was the coronial inquest in 2003, which basically had an open finding.

``As we stand here today we're still not sure what happened to Nancy.''

The witness was at the tip yesterday to help police locate the trench believed to hold the bike.

Detective Inspector Flude said police were not looking for a body at this stage but would expand the dig if the bicycle was located.

``This is our strongest lead,'' he said.

Nothing was unearthed after a full day of searching yesterday and police are expected to reassess the search effort this morning.