Bones found in Philadelphia's "house of horrors," sources say

Bones were discovered outside the so-called house of horrors in the Olney section of Philadelphia, but it's unclear whether they are related to the ongoing investigation into Raymond "R.C." Horsch, a suspected serial killer who died last year, sources told CBS News Philadelphia on Thursday. 

The Philadelphia Medical Examiner's Office responded to the house at 417 West Chew Ave. on Thursday, sources close to the investigation confirmed. 

The bones were found in the backyard, where agents and detectives have been painstakingly searching for any sign of human remains and any evidence of at least seven women connected to Horsch and the house, some of whom are feared dead, sources told CBS News Philadelphia. 

It's not clear whether they were human or animal bones, sources stressed. More testing is needed to determine the bones' origin and whether they are connected to the investigation.

Richard Marx, a retired FBI supervisory agent who specialized in evidence collection, said the presence of the medical examiner is a significant development. 

"If they find something related to the body, then that's when they would want to call the medical examiner, bring them aboard, have them collect it, and have them take it to their office for examination," Marx said.

Investigators have been methodically sifting through the soil in layers, going down about 3 feet.

Investigators found human DNA when they used luminol to search the home, police sources confirmed earlier this week. 

A source also said investigators had found opossum carcasses near the house. The remnants of a brick outhouse were also uncovered in the yard.

The investigation at the house is expected to continue until at least the middle of next week, sources said. Investigators are set to dig up the front yard when they are finished in the back.

Investigators believe Horsch used a process known as alkaline hydrolysis to dispose of bodies, law enforcement sources said. He detailed the steps in one of his books in which he called himself an empathetic serial killer. Chemicals found in the home have been sent to laboratories for testing.

Before his death, Horsch lived in the house with his son, Eugene, whose arrest during a traffic stop in June kicked off this massive investigation. 

Stay with CBS News Philadelphia for ongoing coverage of this investigation and follow on YouTube for extended "House of Horrors" coverage every Friday.