There are a lot of sources of free online police training. The training can take many forms including simply providing the resource materials for you to do your own research and discovery.
The National Criminal Justice Reference Service (NCJRS) is part of the federal government’s alphabet soup of projects that is likely unnoticed by most people. However, just because it isn’t well known doesn’t mean it is not valuable. NCJRS works closely with the Office of Justice Programs including the Bureau of Justice Assistance, National Institute of Justice and Office for Victims of Crime.
The NCJRS maintains an extensive library of criminal justice research studies, abstracts and publications. The studies range from the reduction of youth violence to the use of medical records in the prosecution of domestic violence cases. I’ve never counted the number of documents in their online library, but there are hundreds, if not thousands.
The documents are available in a variety of formats, with the majority in PDF format. Some of the documents can be ordered if you want a hard copy, but all can be downloaded instantly.
If you ever need to research a topic, check the NCJRS out.