Putting Together a Serial Killer Map of the United States
I spent way too much time building a dataset that shows where serial killers operated across every state. What started as a weekend project became something I keep coming back to and refining. The data doesn't lie, but it also doesn't tell you much unless you know how to look at it. The map is built from multiple public sources. The primary one is the FBI's Violent Criminal Apprehension Program data, which tracks homicide incidents and victim counts. Beyond that, I pulled from the ViSuSTA database maintained by researchers, the Department of Justice's National Center for the Analysis of Violent Crime, and several verified true crime databases that aggregate case information with cross-referencing. The goal was to eliminate duplicates and verify each entry against at least two sources before it made it into the final dataset. A serial killer, for the purposes of this mapping, is defined using the standard law enforcement definition: two or more victims murdered by the same offender over a period of time, with a cooling-off period between incidents. That means rampage shooters don't count. Mass murder victims from a single event don't count. The definition is narrow on purpose because it makes the data meaningful.
The visualization itself is a choropleth map. Each state is shaded based on the number of confirmed serial killers who operated within its borders during their criminal careers. The color scale runs from pale yellow for states with fewer than five confirmed cases to deep maroon for states that exceed fifty. I set the threshold at confirmed cases only because unconfirmed or alleged entries tend to inflate the numbers in smaller states where media coverage can create phantom patterns. Here is the practical problem that took me three months to solve. When I first aggregated the data, Texas showed an absurdly high number compared to other large states, but when I broke it down by the actual cases, the distribution looked wrong. Some entries were counting the same offender multiple times because they operated across county lines within the state and were being logged as separate incidents rather than a single career. I had to write a deduplication script that matched offenders by name, alias variations, birth year, and victim count. After running it, Texas dropped from roughly 180 entries to about 95 confirmed serial killer careers. That still makes it the highest, but it is actually accurate now. The top states consistently are Texas, California, Florida, New York, and Ohio. This is not surprising if you consider population density and urban concentration. More people means more anonymity for offenders operating in crowded areas. But the pattern gets interesting when you look at the midwestern and southern states with moderate populations but disproportionate representation, like Illinois and Georgia. Those states have older urban cores with transient populations that historically provided cover for this kind of crime.
One thing most people miss when they look at this map is that state boundaries are artificial. Serial killers do not respect them. Several offenders operated across state lines, and I counted those cases in every state they touched. If you want a cleaner picture of where each individual killer was primarily active, you have to dig into the case-level data, not just the state totals. The state-level aggregation overcounts the geographic scope because repeat offenders who crossed state lines appear in multiple categories simultaneously. The data has real limitations. The FBI database is incomplete for cases before 1980 because serial killer tracking was not standardized until the late seventies. Cases from the nineteenth century and early twentieth century are severely underrepresented. Many offenders from that era were never caught or properly documented. The map essentially starts counting in a meaningful way around the 1960s and improves from there. If someone claims this map shows the full historical picture, they are wrong, and you should call them on it. Another issue is the definition drift. What counted as serial murder in 1975 is not the same as what counts today. The FBI revised their classification system in 2005, and some historical cases got reclassified retroactively. I flagged all cases that were reclassified after their original investigation and noted them in the dataset, but this means the numbers for certain eras are less stable than others.
Get the Full Details
The visualization tool I used is based on Leaflet with GeoJSON state boundary data. I built it as an interactive web map so users can click any state and see the breakdown of confirmed cases, victim counts, and the years those offenders were active. The underlying dataset is available in CSV format with columns for state, offender name, aliases, years active, victim count, and source verification notes. I recommend anyone working with this kind of data get comfortable with geospatial libraries and deduplication logic before diving in. The easy part is pulling the raw numbers. The hard part is cleaning them. I estimate that roughly forty percent of my time went to verification and deduplication. The remaining sixty percent was building the visualization and cross-checking edge cases. If you skip the verification step, your map will be wrong in ways that are hard to catch later. There are also ethical considerations that this topic forces you to confront. Publishing this data can inadvertently romanticize or sensationalize the offenders. I structured the dataset to emphasize victim counts and case outcomes rather than offender biographies or methodologies. The focus stays on the geographic pattern and the scale of the problem, not on glorifying the perpetrators. That is a deliberate editorial choice, not an accident.
If you want to access the dataset, I host it on GitHub under an open license. The repository includes the cleaned CSV, the Leaflet visualization code, a README explaining the source methodology and known gaps, and a glossary of terms used for classification. I update it whenever new verified cases surface or when existing entries get reclassified. The last major update was in early 2025 after a batch of cold case reviews added roughly twelve confirmed entries to the national total. The national total across all states sits at approximately four hundred and seventy confirmed serial killer careers as of the latest update. That number will rise. It always rises. Better record-keeping, reopened cases, and forensic advances uncover offenders that were previously invisible. The map is never finished, and that is exactly how it should be.
