(Bloomberg) -- The heirs of Petr Kellner filed a lawsuit in Alaska over the backcountry helicopter crash that killed the Czech billionaire and four other people two years ago.

In the suit, widow Renata Kellnerova and her family are seeking to investigate “potential negligence” that led directly or indirectly to the fatal crash by the helicopter operator as well as by participants in the rescue mission, their company PPF Group NV said in a statement on Sunday.

The family, which has a net worth of $12.4 billion according to the Bloomberg Billionaires Index, originally wanted to withhold legal action until the publication of the official report into the accident by US authorities, according to the statement. 

But since the investigation hasn’t been completed, the family filed the paperwork days before the two-year statute of limitations expired on March 27. 

Read more: Billionaire Kellner Family Shifts Focus Back to Europe From Asia

The family owns 98.9% of the investment company with assets totaling more than 40 billion euros ($43.4 billion) in industries including financial services, telecommunications, media, engineering, biotech and real estate. Kellnerova is the largest shareholder with a 59.4% stake.

Then aged 56, Kellner died when an Airbus AS350 B3 chopper went down near the Knik Glacier. He’d been on a heli-skiing vacation at a remote luxury lodge located a 40-minute flight from Anchorage. 

Kellner began building PPF shortly after the fall of communism during the sale of state assets in a voucher-for-shares program, eventually becoming the Czech Republic’s richest person.  

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