Evil Doctor could have dissolved the remains, or found a way to dispose of the Human remains.
No, they were the serial killers’ trophies
“they were the serial killers’ trophies”
Exactly. A common thread among serial killers is that they hold on to trophies so they can re-live the pleasure of their evil deeds. This guy is no different. Instead of an earring or handkerchief, he kept the actual humans.