Agencies that are involved in the criminal justice often operate a data or research arm. You can find agencies at the federal and state level, and some regional or city jurisdictions may offer their own portals with more detail available.
Research institutions like universities or think tanks may studies issues related to criminology or victimization and provide original data or research to the public.
Nonprofit organizations that advocate for or support causes may conduct their own research, or they may provide useful research roundups or summary statistics from other sources.
Criminology and victim researchers at universities publish their research in scholarly, peer reviewed journals. This research can be easily found in the library's databases. These researchers may collect their own data in smaller (or big) research projects, or they may use large datasets that are made available by government agencies or in repositories like ICPSR.
News Sources and Websites (and tracking down primary sources)
Other general websites and newspapers or magazines may publish articles which present crime and victim data, or report on the results of research being conducted by other entities, but they rarely are responsible for that research. Hopefully, these sources provide links to the original sources. Agencies that provide fact sheets may be reporting on their own research and summarizing it, but many organizations will collect data points from other sources. For many published reports or fact sheets, they may include parenthetical citations or footnotes/endnotes. To track these down, you'll have to identify the full reference in the works cited list and then identify the source. Then its a matter or searching the library's collection or a search engine to track down the original source.