I want to submit an anonymous tip to Immigration USCIS about fraud in an asylum case. Please advise how to do so anonymously.

I am aware there is fraud going on in a pending Asylum case. The whole family came here in early 1992 with inspection using visitor visa's & they overstayed. In their Asylum story they said they ran across the San Diego/San Ysidro border. This is a lie, but that's what their story was. They were granted Asylum but their attorney got arrested for fraud. The family had their Asylum status terminated when the lawyer confessed. They re-applied using a different attorney & were able to get Asylum again. Our kids went to school together. I recently saw their case on Justia.com and was shocked at the lies they told. They claim they entered USA illegally in October 1992, but our kids went to school together in April 1992. I want to tell USCIS about their fraud. How can I mail them anonymously?