However, I have found it separately. (Resources section may need to be updated.)
Thanks Rick, yes it’s the Introduction to Security Processes whitepaper,
The Security Processes whitepaper is now archived (from January 2020). The corresponding new whitepaper is called "Introduction to AWS Security".
sorry, the correct title is "Amazon Web Services: Overview of Security Processes" (https://d0.awsstatic.com/whitepapers/Security/AWS_Security_Whitepaper.pdf)
The referred Whitepaper "Instroduction to Security Processes" can be found here: https://d0.awsstatic.com/whitepapers/Security/Intro_Security_Practices.pdf