Authorities in Los Angeles County began searching a landfill Monday for evidence related to the disappearance of a woman who vanished in October.

Detectives with the Los Angeles Police Department, along with other agencies, served a search warrant for a specific area of the Chiquita Canyon Landfill in Castaic, 40 miles northwest of Los Angeles. They will be looking manually for human remains and other evidence related to the disappearance of Heidi Planck, the LAPD said. 

Fox News has reached out to the police.

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Heidi Planck (Jim Wayne)

Planck, 39, was last seen Oct. 17 when she left her son's football game in the Los Angeles suburb of Downey before it ended. Her family reported her missing three days later after she failed to pick up her 10-year-old son from school. 

Authorities said she was last seen at a high-rise residential apartment building in downtown Los Angeles. Her dog was later discovered on the 28th floor of the building. 

Evidence found in the building led investigators to believe something happened that resulted in her death, police said. Planck had no connection to the building, her ex-husband, Jim Wayne, previously told Fox News. 

On Nov. 4, her 2017 Range Rover was found in the underground garage of another residential building a few blocks from the one where her dog was found, the LAPD said. Further investigation led them to the landfill. 

The LAPD has not released any suspect information. 

Heidi Planck's dog was found in a residential building in downtown Los Angeles.  (Jim Wayne)

Wayne said he believes Planck's job may have played a role in her disappearance. He said he received a call from a Securities and Exchange Commission (SEC) official on Oct. 21 asking him what he knows about her boss, Jason Sugarman.

Sugarman and his business partner, Jason Galanis, were charged in 2019 with stealing millions from clients.

Planck worked as a controller and executive assistant for Camden Capital Partners LLC, an investment advisory firm under investigation by the SEC. She told her friends that the company had some tax filings due and she complained that her name was on much of the paperwork, Wayne said. 

Heidi Planck seen on surveillance video. Authorities began searching a landfill north of Los Angeles on Monday for human remains and evidence related to her disappearance.  (LAPD)

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The LAPD said a search of the landfill could take seven to 10 days to complete. 

Fox News' Audrey Conklin contributed to this report.