Hatton Garden jewellery raider Terry Perkins has died in HMP Belmarsh, a prison service spokesman said on Monday.
It comes days after a court was told another of his co-offenders, who are all in their sixties and seventies, was also likely to die behind bars.
Last week a court heard Perkins, 69, had been diagnosed with severe heart failure as a judge ordered the four ringleaders of the heist to pay back £27.5 million or each face another seven years in jail.
Perkins’ lawyer, Peter Rowlands, said his client’s flat in Portugal would have to be sold, but said Perkins’ would have to serve the default sentence as there was “no prospect” of any further funds being recovered to settle his £6.5 million debt.
Perkins, along with John “Kenny” Collins, 77, and Daniel Jones, 63, were sentenced to seven years in prison and Brian Reader, 78, was jailed for six years and three months for their roles in the notorious burglary in 2015.
Tom Wainwright, representing Reader, told the court last week that his client’s sentence “does not have to be very long for it to mean, in reality, he will serve the rest of his life in custody”.
Reader has prostate cancer.
Judge Christopher Kinch QC said the men benefited from nearly £14 million worth of cash, gold and gems stolen from boxes at Hatton Garden safe deposit in London’s jewellery quarter after a drill was used to bore a hole into the vault wall.
At a confiscation hearing at Woolwich Crown Court on 31 January, the men were each ordered to pay back millions of pounds based on their “available assets”.
Handing down his ruling, the judge said: “A number of these defendants are not only of a certain age, but have in some cases serious health problems.
“But as a matter of principle and policy it is very difficult to endorse any approach that there is a particular treatment for someone who chooses to go out and commit offences at the advanced stage of their lives that some of these defendants were.”
Collins, of Islington, north London, was ordered to pay £7.7 million after the court heard he had assets in “liquid form” and property in this jurisdiction and abroad.
Jones of Enfield, north London, was ordered to hand over £6.6 million.
His barrister, Graham Trembath QC, said Jones’ only assets were cash in a bank account and he “will have to serve the default term”.
Reader, who was not in court, was told he must pay back £6.6 million including the sale of his £639,800 home and development land worth £533,000.