Like Alfred Hitchcock says on the trailer for Psycho,

"Good evening. I have some news that will delight you. Murder is not dead. I do not refer to the ones splashed all over the front pages. Those are in such bad taste. I refer to those exquisite murders that have a touch of the bizarre, and which take fiendish ingenuity to solve. Those are alive and well."

Some crimes/criminals simply transcend the circumstances in which they were committed, take Jack the Ripper or Ed Gein for example, and are destined to become the stuff of legend. The ghoulishness of DeMeo's crimes ensured him a certain perverted degree of immortality, hence the idea of a Gemini Lounge museum. Like how Scotland Yard maintains its own "black museum." That sort of thing.