The employee filed a suit under whistle-blower laws known as a qui tam lawsuit.
If the lawsuit results in money for the State of New York, then the whistle-blower will be entitled to a share of that money. This is believed to be the first such case in New York that has not been filed under seal.
These suits are obviously rare. It shows that if you are going to try to deceive the government about your residency for estate tax purposes, you might not get away with it if someone else knows about it.
An estate planning attorney can advise you on proper estate tax filing.
Reference: Wills, Trusts & Estates Prof Blog (Jan. 25, 2018) "Suit is Filed in NY's First Unsealed Qui Tam Estate Tax Case."