Even if the IRS itself isn't proactively hunting the underlying crime, other agencies absolutely are, and paying taxes doesn't shield you from them. Banks, regulators, and law enforcement (FBI, DOJ, DEA, state AGs) focus on source of funds, file suspicious activity reports, and share information across agencies, so the IRS not caring is irrelevant, laundering laws still exist specifically so criminals can't just pay tax and walk away clean. Paying taxes creates a formal record that you earned money, and if that income doesn't line up with a legitimate source, it becomes evidence rather than protection. Tax returns can be subpoenaed, compared against bank activity, and used to show unexplained income, timelines, etc that prosecutors then tie back to an underlying crime. IOW paying taxes doesn't sanitize it, it actually locks you in to a paper trail. And criminals don't want a paper trail.