Investigators say Horsch’s ex-wife, Amy McHale, was reported missing in 2016 and was also last seen at the home.
Despite extensive searches, investigators have not recovered any bodies.
Before his death last year, Horsch created violent pornographic films and self-published several books in which he portrayed himself as “an empathetic serial killer”.
In a 2013 interview discussing his work in the adult film industry, he described himself as “a perverted serial killer”.
Videos recovered from the property show Horsch carrying out acts of violence against women, including footage police allege depicts him strangling a woman with a zip tie.
Detectives are now working to determine which scenes were staged and which may provide evidence of criminal offending.
The investigation began in June after Horsch’s son, Eugene, 44, was arrested on weapons and drug charges.
Authorities say he was found with a woman carrying a fake identification card belonging to one of the missing women.
Searches of the Olney property uncovered a vast trove of digital evidence, along with chemical vats, urns and what investigators described as a basement laboratory.
Police believe some of the material belonged to Horsch, a convicted methamphetamine producer, who lived at the address until his death at age 82.
Decades before settling in Philadelphia, Horsch lived in South Canterbury under the name Stanley Stokowski.
He emigrated to New Zealand with his wife and young son, settling in Clandeboye near Timaru, where he helped establish an ethanol plant while presenting himself as an American scientist.
CBS News reported today that FBI investigators had returned to the Olney house, with an inflatable tent erected outside and the surrounding area cordoned off for a fresh round of forensic examinations.
Philadelphia Police Department
Sources told the broadcaster investigators were “looking at everything in the home”, including flooring, drywall and plaster.
It is understood sections of the interior will be removed and tested as authorities follow leads emerging from their review of the extensive cache of videos and images recovered from the property.
Sources have also said detectives have been scouring the property for evidence of wet cremation – a process using a mix of chemicals to break down human remains.
And they will spray luminol in a bid to reveal blood invisible to the naked eye.
Philadelphia police confirmed heavy machinery would be used to excavate the property and investigators were expected to “remove any areas or furniture in the house that could have blood, tissue, hair or other fibres”.
This phase of the search is expected to continue until late October.
Inspector Raymond Evers previously described the evidence found in the house so far as “graphic and dark”.
So far, authorities have sent up to 20 containers of unidentified chemicals seized from the property to a specialist laboratory in Chicago for forensic analysis, CBS News reported.
Police are continuing to examine physical evidence, digital files and sewer systems beneath the home as they work to determine what happened to the missing women and provide answers to their families.
CBS said Eugene Horsch’s lawyer has declined to comment on the investigation – but did say his client was “upset the house will … be destroyed due to the police activity”.
Possible serial killer’s NZ life
Before the events now under investigation in the US, Horsch spent time in the South Canterbury town of Clandeboye, near Timaru, under an assumed identity.
He was known as Stanley Stokowski, an apparent American chemist and computer expert who helped establish an ethanol plant before disappearing from New Zealand.
In 1984, the Press reported that Horsch came to New Zealand under the name Stanley Stokowski – allegedly stolen from an actual Californian scientist.
He reportedly travelled to Canterbury in 1980 with his “wife Anna and 18-month-old son” and helped Christchurch lawyer John Rutherford set up Chemical Technology Limited – a company doing advanced work in byproducts from milk.
Rutherford was said to have contacted Horsch “after reading American advertisements about new technology”.
He told the Press that Horsch was “brilliant and hard working” and “trained unskilled men in skills from welding to more complex tasks”.
In March 1984 Horsch landed on the police radar when he returned from a holiday in the US with several passports.
He fled New Zealand on March 17 on a different passport – which police believed had been stolen from a Temuka house during a burglary.
Police here and in the US, along with Interpol, began a search for Horsch.
After his disappearance, rumours swirled about his true identity, including that he was a Russian or Bulgarian spy, that the CIA was looking for him, and that he was wanted in the US on drug charges.
Rutherford conceded his business partner may have been hiding under a bogus identity, but was nonetheless “a brilliant chap and knew what he was about”.
“He believes that ‘Stokowski’ had had some sort of trouble in the US; perhaps of the scale of being a draft dodger during the Vietnam War,” the Press reported.
“He might also have more serious problems there, but Mr Rutherford dismisses any suggestion that he might be a spy.”
Rutherford described Horsch as a “particularly smart fellow, a real toiler and an excellent family man”.
He maintained he did not hear from Horsch after he left New Zealand. His business did not suffer as a result of the man’s disappearance.
“As far as I am concerned, it is business as usual,” he said.
In April 1985, Horsch was jailed for four years for drug offending in Philadelphia.
The Philadelphia assistant District Attorney confirmed at the time that Horsch pleaded guilty to two counts of possessing methamphetamine for supply and running a methamphetamine laboratory.
The Associated Press reported: “The offences occurred in 1977, but Horsch skipped bail and later spent three years in New Zealand. He left New Zealand in June last year and was arrested in Florida in October.
“He was sentenced on Thursday to three years’ jail on the drug charges and a consecutive term of one year and one day after admitting the bail-jumping offence.
“After his release, he will be on special parole for two years. If he reoffends during that period, he would be recalled to prison to serve the five-year maximum term of imprisonment for the charges.”
Around the same time, Horsch was named in a case in the Wellington High Court involving an alleged $18,000 credit card debt.
An investigation was carried out into how Horsch and his family were allowed to live in New Zealand.
It concluded that “normal and correct immigration procedures had been followed” and Horsch’s “papers” – in his stolen name – supported his application and included a transcript of a university degree.
The real Stokowski later confirmed the transcript was his.
The investigation report stated the Department of Immigration at the time was “under some pressure” from Horsch’s “proposed employer” to “make an early decision”.
“The application indicated that the man claiming to be Dr Stokowski possessed special skills in the development of alternative fuels,” media reported.
”Checks were not made with the Ministry of Energy and other Government departments … Nor had the man been interviewed by the New Zealand Consulate-General in San Francisco, as was now the proper practice.
“It was unlikely that anything amiss would have been discovered. All supporting documentation appeared to have been altered to match the applicant’s identity.”
US media have reported that Eugene Horsch remains in federal police custody on drug and firearms charges.
Police confirmed that investigators had not found evidence that connected him to any of the dead or missing women.
Anna Leask is a senior journalist who covers Christchurch issues and national crime and justice. She joined the Herald in 2008 and has worked as a journalist for more than 20 years with a particular focus on family and gender-based violence, child abuse, sexual violence and homicides. She writes, hosts and produces the award-winning podcast A Moment In Crime, released monthly on nzherald.co.nz.