MADISON, Wis. -- A muddy, weeklong search of a Juneau County landfill has turned up no new evidence in the 30-year-old investigation of a missing Madison woman.

Madison police said that they finished searching a small area of the dump around noon on Friday.

Authorities were looking for Jean Zapata's human remains and some containers, which police thought to be placed there a year ago, WISC-TV reported.

The investigation, long a cold case, is now an active murder investigation.

One of Zapata's daughters who still lives in the area said that the lack of evidence found at the landfill is "disappointing" and "frustrating," but she remains confident that police will ultimately succeed.

Zapata was a 36-year-old Madison woman and mother of three who mysteriously disappeared from her home in 1976.

Police said that they are acting on a tip that led them to the landfill located off Ceylon Road.

The landfill search follows earlier ones in which cadaver dogs picked up the scent of decomposing human remains at Zapata's former Madison home and at a Sun Prairie storage locker last year.

Police have called Zapata's former husband their only suspect and executed three search warrants at his Nevada home in November. However, Eugene Zapata said that he had nothing to do with her disappearance, WISC-TV reported.