Tax Obligation

[Isobelcb]

How do I notify the IRS that a home owner kept $33,000 of a failed home purchase. The money was the down payment. I have a  work sheet from them showing that they used the money to pay their mortgage and the difference in the price that eventually got when their home sold to a different buyer. I know they did not know they have to pay tax on it because our realtor did not know. The work sheet did not allocate money for tax. I have their name, previous address but not their SS#. Can I just send in the  worksheet signed by them to the IRS. I feel strongly they should not get $33,000 free money. 
thank you

[bbaker11]

If you suspect or know an individual or business isn't complying with the tax laws or hasn’t paid the tax they owe, report online or by mail with Form 3949-A, Information Referral. Tax fraud also includes: false exemptions or deductions, kickbacks, false or altered documents, unreported income, organized crime and not withholding required taxes.