Crime boss Willem Holleeder is likely to spend the rest of his life in prison after losing his final appeal against his conviction for ordering five contract killings.

The Supreme Court dismissed claims by lawyers for Holleeder that his original conviction was based on testimony from unreliable witnesses, including fellow gang members Peter La Serpe and Fred Ros.

The 65-year-old was also implicated by his two sisters, Astrid and Sonja, who have lived under heavy protecting since they gave evidence against him during an 18-month trial that ended in July 2019, when he received a life sentence.

The supreme court judges followed the advice of the advocate-general, who said in November that the reliability of the witnesses had been sufficiently tested and the deals with crown witnesses were legally sound.

Holleeder became a celebrity during the 1980s when he masterminded the kidnapping of beer magnate Freddy Heineken for a ransom of 35 million guilders – equivalent to around €35 million in today’s money. Some 8 million guilders was never recovered.

One of his later victims was his brother-in-law and close collaborator on the kidnapping, Cor van Hout, who married Sonja Holleeder. Four other criminal associates – Kees Houtman, Thomas van der Bijl, Willem Endstra and John Mieremet – were murdered on Holleeder’s orders between 2003 and 2006.

Astrid Holleeder told gossip show RTL Boulevard that she was “relieved” the long-running case had been concluded. “I hope the friends and relatives of all those involved can now find peace,” she said.