Scotland's First Minister Alex Salmond has told ITV News the Jim Clark Rally crash that left three people dead and two others critically injured was "an extraordinary incident of great severity".
Mr Salmond said: "These are tragic circumstances and obviously all our hearts go out to the people who have been killed and injured.
"Given the extent of this tragedy, people can be reassured the [investigation] process will be complete and thorough".
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His representatives said Cassidy, who was hospitalised last week, died "surrounded by those he loved."
The company’s recently appointed Chief Executive Dara Khosrowshahi said the breach was made by two individuals outside the company.