I'm an accountant, and used to prepare tax returns for those who were arrested for drug dealing. Back in the 1990s I worked at an accounting firm a criminal defense attorney would send his clients to, in order to avoid tax evasion issues.
First, you cannot make illegal money legal. Attempting to do so is money laundering, which is another crime. Illegal income is taxable, though, so if you pay taxes on the income you would not be charged with tax evasion.
To file the tax return, you need to go through an attorney. That is because financial advisers, accountants, including CPAs, do not have privileged communication. Without going through an attorney, an accountant must reveal whatever you told him about your illegal income (if the preparer is issued a subpoena).
As a side note, illegal income is taxable, but illegal expenses cannot be deducted. Consequently, you would pay both regular income tax and self-employment tax on the gross amount of your income from criminal activities.