I'd love to find a perfect opportunity like that house. I'd make a point of seeking them out (not just murder-scene houses, but any other house that people pretend has less value for no reason at all) if I knew of a way to do so, and if I believed there were enough of them.
This was a very high profile case.
The girl was missing for several days. Her picture all over the media. many people felt empathy for her and her family.
Then it turned out that the killer was neighbour, living a couple of houses away.
The guy was a cop, which again made it a continued media event.
then it came out that he had buried her in the garden had literally given a BBQ on top of her grave.
When the house came for sale it made front pages of the sensationalist news outlets. There are so many prospective buyers that it will probably go for the normal price.
But one could certainly make use of the psychological reaction to horrific events and snap up cheap real-estate.
I actually suspect that the shock effect will wear off and if a normal family lived a happy life in it for ten years, the house will probably be perceived differently by subsequent prospective buyers.
That Gestapo villa looked positively spooky for years, now that it is in use the horror atmosphere had subsided in my view. (and in this case the architecture was spooky to begin with, it looks like a good setting for the next Bates Motel).