Earlier quoted context omitted.
The IRS explicitly states that you need to declare bribes and income from illegal activities [1] "Illegal activities. Income from illegal activities, such as money from dealing illegal drugs, must be included in your income on Form 1040, line 21, or on Schedule C or Schedule C-EZ (Form 1040) if from your self-employment activity." [1] https://www.irs.gov/publications/p17/ch12.html
That's just hilarious! Are you saying drug dealers actually report their income and pay taxes off it?
In some cases proving tax evasion is easier than proving other crimes. This is what got Al Capone -- because the crime was perpetrated through his organization and not by him directly, it would have been difficult to hold him directly responsible for the crimes. However, once his ledger was discovered it was straightforward to prove that he received significant income without making the required income tax payments.