“This is a momentous day in Autonomy’s history,” Mike Lynch declared in a press release on 18 August 2011. He was announcing the sale Autonomy, his software firm, to Hewlett-Packard for $11bn.

For Lynch 6 June 2024 would prove more significant.

After a saga spanning almost 13 years, Lynch – once dubbed “Britain’s Bill Gates” – was cleared of fraud following a lengthy trial in the heart of Silicon Valley. The verdict amounts to a stunning reversal in fortunes for the entrepreneur.

On Thursday, Lynch said he was “elated” to have been found not guilty. “The truth has finally prevailed,” his lawyers declared.

He now plans to fly home to the UK, where he still faces a fight to clear his name. HP largely won a civil lawsuit against Lynch and Sushovan Hussain, another top autonomy executive, in London two years ago. The company is seeking $4bn in damages. Lynch has previously indicated he plans to appeal the ruling.

By all accounts, the takeover was disastrous. Just five weeks after it was announced, the HP CEO who signed off on the deal was sacked. Lynch departed Autonomy after less than a year. The lucrative takeover had fleetingly cemented Lynch’s reputation as one of Britain’s most successful tech tycoons. Its real legacy was more than a decade of acrimonious legal wrangling.

In November 2012, HP’s new management wrote down the value of Autonomy by $8.8bn, alleging “serious” accounting improprieties, disclosure failures and “outright misrepresentations” before the purchase. After years of investigations and legal proceedings on both sides of the Atlantic, a US federal grand jury indicted Lynch on criminal charges in November 2018. After the civil case concluded, the UK agreed to extradite him.

His legal problems mounted last year. Having largely lost the UK civil lawsuit, Lynch lost a UK high court bid to appeal his extradition. Weeks later, he was on a plane to California.

This San Francisco trial, on more than a dozen counts of fraud, amounted to a steep climb for Lynch, who unsuccessfully fought to avoid extradition to the US. Federal prosecutors have a fearsome record of guilty verdicts, and Lynch’s lawyers were forced to adjust their defense ahead of the trial.

From the start of this saga, Lynch insisted Autonomy’s unravelling was the result of HP’s mismanagement of a prized asset rather than fraud. But the US district judge presiding over the trial, Charles Breyer, barred Lynch’s lawyers from presenting evidence which they said made this case.

Unable to focus on the aftermath of the takeover, Lynch’s defense was built upon on three key arguments: first, that running a business like Autonomy is far more complicated than prosecutors would have the jury believe; second, that Lynch was a far different man to the character he had been portrayed as; and third, that HP rushed to seal the deal, racing through due diligence.

The government’s case was “black and white”, Reid Weingarten, one of Lynch’s attorneys, declared in the opening days of the trial. “And you know what? You’re going to see in this trial that ain’t the way the world works. The world works in grey. The world is complicated.”

Life is “nuanced, and it is messy”, Lynch told the court, suggesting his trial was effectively “peering through the door and seeing the sausage being made. One thing to bear in mind is if you take the microscope into a spotless kitchen, you will always find bacteria. And I don’t think Autonomy is any different.”

Prosecutors tried to paint Lynch as an intimidating, ruthless businessman who was responsible for every facet of Autonomy’s empire. Jurors heard about the piranha tank in the atrium of the company’s headquarters, and meeting rooms named after James Bond villains.

Lynch found it “surreal” to hear government witnesses testify about many discussions and decisions of which he said he had not been aware. He said he delegated jobs where he had no expertise, and in his latter years at Autonomy spent “about 30%” of his time with family and on other interests.

“We believe the better you know him, the better off we are,” Weingarten told the jury, before Lynch testified.

Prosecutors said Lynch had “500m reasons” to commit fraud – one for each of the pounds they claimed he had earned the HP’s takeover of Autonomy. But the company had wanted to remain independent, according to Lynch.

It was one of the stars of London’s FTSE 100 share index, and still pursuing its own acquisitions. By Lynch’s telling, it was only a meeting with an HP executive at a luxury house in the English countryside which persuaded him to start considering a deal – and a 64% premium on Autonomy’s stock price that ultimately prompted the company to accept.

HP was so determined to expeditiously transform itself from hardware manufacturer to software giant, Lynch claimed, that the first time he saw the press release announcing its takeover of his company was when it was released. The process was a “complete mess”, he reflected on the stand.

The prosecution argued HP’s handling of the process was irrelevant. For years, they alleged, Lynch had orchestrated a huge fraud and Autonomy had used a variety of accounting tricks to inflate its sales growth.

But Lynch stressed that HP was “not at all” misled about Autonomy’s value. A jury of Californians believed him, rejecting the case laid out in great detail by the US government, which summoned more than 30 witnesses.

Six years ago, in the same court, a jury came to a different conclusion about one of Lynch’s closest business partners. Hussain, who worked as Autonomy’s chief financial officer, was convicted in 2018 on charges of conspiracy, wire fraud and securities fraud related to the deal. He was released from a US prison in January after serving a five-year sentence.

Lynch, who at the height of his career was awarded an OBE (Order of the British Empire) and advised the UK prime minister, spent much of the year before his trial monitored by two armed guards around the clock, under effective house arrest. The specter of more than two decades in prison, were he convicted, loomed large.

On Thursday, the businessman left court a free man. “I am looking forward to returning to the UK and getting back to what I love most: my family and innovating in my field,” he said.

Another momentous day.