Mike Lynch, the technology tycoon, once dubbed Britain’s Bill Gates, has spent the past 10 months in San Francisco, with a GPS bracelet strapped to his ankle and two armed guards monitoring him around the clock. This week he heads to court to face a long, hard fight for his freedom.

It’s been 13 years since one of Silicon Valley’s most storied companies bought Lynch’s business in a blockbuster takeover that seemed to confirm his image as one of the UK’s most brilliant technologists. Now that deal is at the center of a criminal fraud trial. If convicted, Lynch could spend up to 25 years in jail.

It has been a stunning fall from grace. As co-founder of Autonomy, a software firm that became one of the shining lights of the UK tech scene, Lynch was lauded for his achievements in business: awarded an OBE (Order of the British Empire) for services to enterprise in 2006, and appointed in 2011 to the science and technology council of the then prime minister, David Cameron. He served on the board of the BBC, and established an investment firm that backed Darktrace, the cybersecurity firm.

Now Lynch is about to embark upon an arduous battle to persuade a jury that the highlight of his career – Autonomy’s acquisition by Hewlett-Packard – was not built on a pack of lies.

The odds against him are high. US federal prosecutors have a fearsome record and most defendants would rather plead guilty than go to trial. Analysis by the Pew Research Center last year found that, of 71,954 defendants in federal criminal cases in 2022, only 2.3% went to trial. Just 0.4% were acquitted.

Lynch, who has pleaded not guilty, will need to dismantle the allegations surrounding how he constructed, led and presented Autonomy to the world. Attention in the courtroom is likely to turn swiftly to one Thursday afternoon in August 2011.

Ten minutes after Wall Street closed for the day, HP revealed a master plan. The world’s largest maker of personal computers had had enough of making personal computers – and wanted to transform from hardware manufacturer to software giant. The only snag was that software was responsible for just 3% of its sales.

Autonomy, a fast-growing and much-hyped software and data company that counted Coca-Cola and Nestlé among its clients, looked like the answer.

HP agreed to buy Autonomy in a £7bn ($10bn) deal to “accelerate our strategic vision to decisively and profitably” dominate the software industry. Léo Apotheker, HP’s CEO, declared its purchase to be “highly profitable and globally respected”, with an “attractive business model” and “well-regarded” management.

For Autonomy, and the man who built it, the acquisition was an extraordinary (and lucrative) endorsement. “This is a momentous day,” said Lynch.

The celebrations didn’t last long. Apotheker was sacked five weeks later, and Lynch departed as Autonomy’s CEO less than a year after the takeover, as his firm failed to meet expectations inside HP. It would not take long for the situation to go from bad to worse.

By November 2012 – just 15 months after the deal was first disclosed – it had rapidly, and disastrously, unravelled. HP, which had ultimately bought Autonomy for $10.3bn, wrote down its value by $8.8bn and alleged “serious accounting improprieties, disclosure failures and outright misrepresentations at Autonomy” before the purchase.

Lynch said he was shocked by the claims. “We flatly reject this; there’s no truth in this,” he told the BBC, suggesting Autonomy had been managed “very badly” by its new owner, which he accused of using these accusations to distract from dismal earnings. “It lost around half of the staff before I left – the whole of the management team – and, you know, the value of that company has now fallen, and they’ve been forced to write it off.”

But HP said a senior Autonomy executive had come forward with concerns that had been substantiated by an investigation. It pledged to “aggressively pursue” the issue, and referred the findings to British and American regulators.

“What we now believe is that this was a willful effort on the part of certain members of Autonomy management to inflate the underlying financial metrics of Autonomy when it was a publicly held company, before HP bought it,” said Meg Whitman, Apotheker’s successor as HP chief executive, “in a deliberate effort to mislead shareholders, and mislead potential buyers of the company.”

Officials in the UK duly launched their own investigation, which was closed in 2015. The Serious Fraud Office (SFO) said there was not enough evidence to secure a conviction, and ceded jurisdiction over aspects of the case to US authorities.

In 2016 the federal government charged Sushovan Hussain, who had served as chief financial officer at Autonomy, with fraud. Hussain, who denied wrongdoing, stood accused of exaggerating the firm’s financial performance and misleading investors. He was convicted in April 2018 on 16 counts of wire and securities fraud, and jailed for five years in 2019 – by which time US prosecutors had turned to focus on his former boss.

In November 2018, a federal grand jury indicted Lynch and Stephen Chamberlain, Autonomy’s former vice-president of finance. The pair was accused of scheming to defraud Autonomy investors, including HP, about its true performance, financial condition and growth prospects.

Lynch sought to fight his extradition. When high court judges in London rejected his appeal last April, a spokesperson for Lynch said he was “very disappointed” by their decision. The following month, he was extradited to the US and ordered in a San Francisco courtroom to pay a $100m (£79m) bond.

Lynch and Chamberlain have both pleaded not guilty. Together they have been charged with 16 counts of conspiracy and wire fraud. Lynch faces an additional charge of securities fraud.

The government plans to call some 44 witnesses. “Since federal prosecutors can choose which cases to bring, and have the resources to follow the evidence wherever it leads, most federal indictments are strong cases that leave defendants with limited options in terms of a defense,” said Robert Mintz, a former federal prosecutor and a partner at law firm McCarter & English. “This results in only a small percentage of federal criminal cases actually going to trial, and an even smaller number ending in an acquittal.”

Since last May, Lynch has been under effective house arrest in a lavish San Francisco home. Only in November was he permitted to leave the property between 9am and 9pm each day, albeit under strict conditions.

The tycoon has been building an argument to present with his team. His lawyers have spent months arguing with prosecutors over the evidence that should or should not be used at trial, and the witnesses who should or should not be allowed to appear.

For more than a decade, Lynch has pushed back against the allegations against him – levelled first by HP, before federal prosecutors stepped in following an investigation involving the FBI, Internal Revenue Service and Securities and Exchange Commission.

This was not fraud, he has argued from the start, but the result of HP’s mismanagement of a prized asset. “They drove out the top 100 people from Autonomy, and a bunch of trainees were put in” to sell its products, Lynch told the New York Times in 2012.

Lynch’s case has already been made in court – and fallen flat. Two years ago, after one of the longest civil trials in English legal history, a judge found he had, indeed, masterminded an elaborate fraud. His defense team has previously indicated he intends to seek permission to appeal against the ruling. Last month HP’s lawyers, seeking to recoup losses, claimed in a London court that the company lost more than $4bn on the takeover.

The US district judge presiding over his trial in San Francisco is familiar with the intricacies of this extensive saga: Charles Breyer also oversaw the trial of Hussain six years ago.

But the outcome of this trial will not be decided by Breyer. Over the coming weeks, 12 jurors will listen to arguments from both sides – and decide who they believe.