Philly and the FBI excavated Horsh's backyard, where seven missing women were tied up in a possible serial killer investigation.

The RC Horsch home in Philadelphia is being excavated again as FBI investigators look into the connection to the seven missing women and disturbing video evidence.

Retired cold case sergeant breaks down the latest in Philly's "house of horrors."

Joseph Giacalone, a retired NYPD sergeant and adjunct professor at the John Jay College of Criminal Justice, said the large number of crime scene technicians at the Olney home of Raymond "RC" Horsch stood out to him.

Police and the FBI have returned to dig up the backyard of a Philadelphia home as part of an ongoing investigation into a potential serial killer that has already turned up revealing "donation" videos, urns filled with ashes and evidence linked to at least seven missing women.

Images show an excavator in a backyard as police continue to walk through the property in protective gear. They have set up tents in the backyard and in front and covered parts of the grass with tarps. Researchers can be seen wearing various levels of safety equipment, including face masks, suits, rubber gloves, protective sleeves and boots.

HAZMAT crew in search of potential serial killer removes 'glass vials' from home linked to missing women

There is yellow police tape around the perimeter and uniformed officers stand guard.

Joseph Giacalone, a retired NYPD cold case sergeant and adjunct professor at John Jay College of Criminal Justice, said the scale of the investigation stood out to him.

WATCH: FBI Evidence Response Team Continues Investigation at Eugene Horsch's Home

Police have visited the home several times in recent weeks and collected boxes of evidence earlier this month, including one marked "glass vial."

A spokesman for the Philadelphia Police Department declined to provide details on Thursday's ongoing search, citing an active and ongoing investigation.

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Raymond "RC" Horsch, creator of pornographic BDSM books, died last year at age 82. However, police searched her former home after her 44-year-old son, Eugene Horsh, was arrested in June. Young Horesh was arrested in a car next to a woman carrying an ID card belonging to one of the seven missing women now linked to the investigation.

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Initial searches turned up images and videos that police said show four of the seven missing women. They also found a barrel of chemicals connected to the home's water system.

Two other women were identified in local reports. Both are listed as missing persons in the National Missing and Unidentified Persons System, or NamUs.

One of them is Horsch's ex-wife Amy McHale, 54, who was last seen on June 13, 2016, the Philadelphia Inquirer reported in June.

The other is Nicole "Nikki" Fusaro, 34, according to the CBS Philadelphia affiliate, citing local police sources. He was 27 years old when he disappeared near the intersection of Kensington and Allegheny streets in July 2019.

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Investigators said they have identified dozens of other people from the images. However, no arrests have been made as the investigation continues.

Police had already dug underground pipes, but no bodies were found.

Eugene Horsh's arrest was unrelated to the disturbing discoveries police made at his father's former home, and he has not been charged in connection with the women's disappearance.

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