The search for a 39-year-old Mid-City mother who has been missing for more than a month has taken detectives to a landfill in Castaic on Monday morning, police said.

Investigators served a search warrant to excavate part of the Chiquita Canyon Landfill, located at 29201 Henry Mayo Drive, as they look for the apparent remains of Heidi Planck and any related evidence in the case, according to a Los Angeles Police Department news release.

Planck hasn’t been seen since Oct. 17, leaving family and friends baffled over her mysterious disappearance and seeking answers.

“We know for sure that there are people out there who know what has happened, who know the truth about what’s gone on with Heidi,” Planck’s ex-husband, Jim Wayne, said at a news conference Monday.

Plank’s last known sighting was when she was captured on a video walking her dog in downtown Los Angeles. The dog was later discovered on the 29th floor of a high-rise apartment building in the 1200 block of South Hope Street.

“Forensic evidence was located inside the building which has led detectives to believe an incident occurred resulting in Planck’s death,” according to the release.

LAPD officials have not indicated how she might have died, nor have they released further information about the forensic evidence they uncovered that led detectives to that conclusion.

Police also said that the missing woman’s 2017 Range Rover was found on Nov. 4 in a different residential parking garage several blocks away from the Hope Street apartment complex.

It’s unclear why Planck was in the downtown area. Hours before that, she had gone to her son’s football game in Downey and left early.

“She didn’t seem agitated. She might have been a little bit antsy. She left with her dog, and she just walked up to us and said, ‘I’m gonna go,’” Wayne said previously.

He was the one who reported her missing to police on Oct. 20.

Wayne believes his ex-wife’s disappearance is possibly related to her work at Camden Capital Partners, as her boss has been charged by the Securities and Exchange Commission in connection with an alleged $43 million tribal bonds scheme.

The SEC contacted him four days after his ex-wife vanished to inquire about Planck’s boss and the company, according to Wayne.

A search warrant was served by Los Angeles police and federal agents at the missing woman’s home in late October, and it may have been related to the fraud investigation.

Police are still gathering leads in the case and stress that, “There is currently no suspect information,” according to the release.

Wayne pleaded for the public’s help to provide information in the case.

“We know for sure that there are people out there who know what has happened, who know the truth about what’s gone on with Heidi,” he said.

The department’s elite Robbery-Homicide Division is investigating the case and is asking anyone who has information related to Planck’s disappearance to call them at 213-486-6840.