BBC Scotland can reveal that a fourth person died in the outbreak of Legionnaires' disease in Edinburgh last summer.
The death of a 64-year-old woman has now been included alongside three other victims.
The Crown Office has asked the police and the Health and Safety Executive to investigate the deaths.
The woman died on 15 July 2012, nearly six weeks after the death of the first victim on 5 June.
The other three victims were men aged 56, 47 and 65. A total of 56 people have been confirmed as having contracted the disease, with a further 36 suspected cases, bringing the total number of people affected to 92.
This is a slight fall from the 101 confirmed or suspected cases when the outbreak was declared officially over on 18 July 2012.
More than a year after the outbreak, an investigation into the cause is still ongoing.
The Legionella bacteria is thought to have been spread across the city in a cloud of vapour from a cooling tower.
Six cooling towers in the South West of Edinburgh were tested and treated, with work concentrating on four towers which were "shock treated" with chemicals.
However, at the time the health secretary Nicola Sturgeon expressed doubt whether investigations would prove beyond doubt which company had caused the outbreak.
A spokesperson for the Crown Office told the BBC it would be inappropriate to comment while an investigation was under way.
A report on how the outbreak was handled by health experts is due to be put before NHS Lothian's health board next Wednesday.
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