https://www.irs.gov/uac/Historical-Documents-relating-to-Alphonse-(Al)-Capone,-Chicago
This link from the Internal Revenue Service gives more information about Capone's finances.

http://law2.umkc.edu/faculty/projects/ftrials/capone/caponetranscript.html
This is the official transcript of Capone's trial in 1931.

https://archive.org/stream/695533-al-capone-fbi-file-1#page/n5/mode/2up
This is one of Capone's official FBI files.

https://www.uic.edu/orgs/kbc/ganghistory/IndustrialEra/caponemap.html
This is a map of areas of Chicago that Capone controlled.

https://archive.org/stream/CaponeFBI/capone10a#page/n65/mode/2up
More newspaper articles about Al Capone.