A Brief History of Open Source Intelligence
By Cameron Colquhoun
https://www.bellingcat.com/resources/articles/2016/07/14/a-brief-history-of-open-source-intelligence

A Tradecraft Primer: Structured Analytic Techniques for Improving Intelligence Analysis
By a CIA/Directorate of Intelligence Analyst
https://www.cia.gov/resources/csi/books-monographs/a-tradecraft-primer/

Bibliography of the most essential sources in Open Source Intelligence
By Arno H.P. Reuser
http://bib.opensourceintelligence.biz

Criminal Intelligence Manual for Analysts
By United Nations Office 
https://www.unodc.org/documents/organized-crime/Law-Enforcement/Criminal_Intelligence_for_Analysts.pdf

Deep Dive: Exploring the Real-world Value of Open Source Intelligence 1st Edition
By Rae Baker
https://www.amazon.com/Deep-Dive-Exploring-Real-world-Intelligence/dp/1119933242

OSINT Techniques: Resources for Uncovering Online Information
By Michael Bazzell 
https://www.amazon.com/OSINT-Techniques-Resources-Uncovering-Information/dp/B0BRDLYX75

Psychology of Intelligence Analysis
By Richards J. Heuer, Jr. 
https://www.cia.gov/resources/csi/books-monographs/psychology-of-intelligence-analysis-2

The Authoritative Guide to Due Diligence by Cynthia Hetherington
https://www.amazon.com/Osint-Authoritative-Guide-Due-Diligence/dp/1960299425
We Are Bellingcat: The Online Sleuths Solving Global Crimes 
​https://www.amazon.com/We-Are-Bellingcat-Sleuths-Solving/dp/1635578477