Morbid Curiosity
The term "thanatourism" refers to visiting regions and sites associated with historical deaths.
This is in contrast with "dark tourism," which refers to visiting sites associated with death, suffering, or other sorts of horribleness—a broader collection of grim associations, basically, compared to the death-centric focus of thanatourism.
Both terms were originally introduced (in academic publications, at least) in 1996, in the same edition of the International Journal of Heritage Studies, and these topics have only seemed to become more relevant in the decades since, due in part to the explosion of interest in what's become known as True Crime-themed podcasts, TV shows, and publications.
As a modern genre, True Crime seems to be massively more popular with women than men, but the concept of engaging in "dark leisure" activities, including visiting battlefields and cemeteries and places where people were tortured or assassinated or otherwise brutalized seems to be fairly broad in its appeal across demographics, and has been associated with what's called "heritage tourism," which ties this interest to a broader interest in establishing historical, cultural, and connective (one's personal connection with a location or group of people, for instance) context.
Another take on the fascination with historical violence and death, though, ties it to what's called "morbid curiosity," rather than heritage-related context-setting.
This tendency to enjoy (on some level) stories and art and ideas that horrify or scare or annoy or disgust us has been the topic of psychological research for generations, and one dominant theory posits that we gain some sort of visceral satisfaction from living variously through deviant people who defy social norms and rules.
A thief, a murderer, or a rapist, then, all allow us to imagine defying convention, taking what we want, and ignoring social mores and laws in our pursuit of fulfilling baser, more brutal and animalistic urges and desires.
Soaking up the details of a series of murders, then, might allow us to explore these urges without engaging with them in real-life, providing us the opportunity to experience an echo of what it would feel like to be that kind of person, without becoming that kind of person and suffering the emotional, physical, and legal consequences of doing so.
There's another evolutionary psychology-linked theory that True Crime and similar explorations tap into our tendency to seek out gossip and other social data points because this information provides us with a survival advantage.
That advantage is, theoretically at least, derived from knowledge about dangerous things and situations we are more likely to avoid if we know the details of what happened to someone else who did not avoid them.
If we know precisely how the victim of a murder was tricked or trapped or whatever else, that allows us to preemptively explore how horrible their experience must have been, which in turn grants us emotional triggers and visceral reminders that could help us avoid the same in the future, alongside raw data about how to not do the same things they did.
This theory is predicated on the idea that we are psychologically rewarded for collecting survival-related information and engaging with it, simulating it our our minds; whatever internal reward systems nudge us toward doing so might then make this type of exploration addictive.
Whatever the source of our tendency toward morbid curiosity, there does seem to be a spectrum of interest in such things, and the popularity of violence-tinged tourism and True Crime (and otherwise violence-themed) genres of everything would seem to imply that modern humans are valanced toward this sort of experience and content, which may suggest it's in some way beneficial to explore such narratives, but might also merely represent a hair-trigger reward system that, to some, can be a bit addictive, despite not being relevant to their real-life experiences or survival-related outcomes.