Start with this online collection of (mostly) reference books. Subject-specific encyclopedias, handbooks, companions, etc.
Think of this as separate questions, and therefore, separate searches. For example, you could look for articles about:
Treat each question as a separate search!
These are reports from Wells Fargo itself, about their own investigations (primary sources in effect). Start with the Key Findings report, since it's much shorter.
HBR has several articles that cover various aspects of this case. Because of contractual limits imposed by HBP on Ebsco and hence on us, no links to individual articles can be created. Therefore, just search on Wells Fargo!
For the ebook below, Flying Blind, please be aware that we were only permitted to buy a single user license. Furthermore, it is not possible to print or download any of this ebook: you must read it online.
Please read what you can in a single sitting, then close your browser window/tab so that others may read it.
Includes some encyclopedia articles and more.
Below are sample resources. But there is a lot more coverage of this case in the popular and business news press. Try searching in the database ABI/Inform Collection to find more.