PHILADELPHIA, Pennsylvania -- Philadelphia police and the FBI will be back at the so-called “house of horrors” Monday night in Olney to continue the investigation into the Horsch residence at 417 W. Chew Ave. U.S. investigators have been coming and going from the Horsch home for months. They work in the daylight, searching for clues of foul play and human remains. On Monday night, they will wait until it’s dark. Law enforcement will look for signs of human blood using luminol at nightfall. “Luminol is a presumptive test for blood,” retired FBI supervisor Richard Marx said. Marx oversaw evidence recovery in some of the most complicated investigations, including Pulse nightclub and the World Trade Center. CBS News Philadelphia asked him about luminol, which is being used in the West Chew Avenue case. “When sprayed on trace amounts of what is believed to be blood, it gives off a very faint luminescence, a blue light,” Marx said. “It has to be relatively dark in the room to see the light because it’s a very faint chemical reaction.” Police sources say they’ve located valuable evidence in their work to uncover what happened to as many as seven missing women tied to 417 W. Chew Ave. and Raymond “R.C.” Horsch, the dead homeowner. His son, Eugene Horsch, remains locked up on drug and weapons charges pending a federal trial. His attorney has declined to talk about the case or comment on whether Eugene has spoken with investigators. Time will tell if detectives are able to find evidence of foul play or traces of blood inside the Horsch residence. Marx said investigators should be able to recover evidence from long ago. “Because items that often retain blood are very porous. They’re almost like a sponge. So, if you have carpet, if you have hardwood floors, they can seep down into the gaps of the floors. So spraying the chemical can often detect blood that is many, many years old,” Marx said. Sources say excavation equipment will be brought in Tuesday to dig up portions of the backyard of the home as the search for any possible human remains continues. By Joe Holden, Alicia Roberts and Tom Gardiner
