Fujitsu, the company that built the flawed Horizon IT system, sacked a top boss at the height of the scandal.
Rod Vawdrey, 67, was dismissed as Fujitsu’s global president in 2014 for personal conduct issues, former colleagues say.
He returned to his native Australia, where he is now being sued for his involvement in a “train wreck” stock market float which made him millions.
Mr Vawdrey told the BBC he wasn’t involved in the Horizon project.
Mr Vawdrey had responsibility for the UK operation from 2011 to 2014 – a crucial time in the Horizon scandal.
If the Horizon issue was discussed by the UK board, Mr Vawdrey must have been aware of it.
Companies House filings say he was executive chairman of Fujitsu Services Ltd, the UK company and sat on its audit and corporate governance committees.
At this time details were beginning to emerge in public, with MPs and journalists raising concerns. But until 2013 the Post Office was still prosecuting dozens of people every year based on evidence from the flawed branch computer system.
Alarm bells were ringing internally too. In 2013, a barrister warned the Post Office that a Fujitsu employee was giving incomplete evidence in court, failing to disclose information about bugs in his witness statements.
This was a crucial turning point in the story, but neither Fujitsu nor the Post Office came clean about problems with Horizon until years later, piling yet more suffering on the hundreds who had been unfairly convicted.
Mr Vawdrey was the only Westerner on the main Fujitsu board, with responsibility for its operations outside Japan, including the UK which was an important market.
Two well-placed former colleagues of Mr Vawdrey told the BBC that he was “terminated for cause” by the company early in 2014. This was due to personal conduct issues, not anything related to Horizon, the sources allege, including running up too many expenses. “Living high on the hog,” as one put it.
One described his management style as “rumbustious”, sometimes shouting at colleagues – either a “bulldog” or a “bully”, depending on which side you were on; the other source agreed.
His tenure was relatively brief – a little more than two years – and Fujitsu’s UK accounts show no record of a departure payment to Mr Vawdrey, unlike the multimillion-pound sums paid to departing bosses before and afterwards.
Mr Vawdrey is not currently due to appear at the Horizon Inquiry, though it will hear from Duncan Tait, who was UK chief executive and reported to him. Foreign nationals can give evidence, but the Inquiry has no powers to compel them unless they return to the UK.
After Fujitsu, Mr Vawdrey moved back to Australia and was involved in another public scandal, which left him a very wealthy man.