What a difference a coup d’état makes. When the billionaire Thaksin Shinawatra, then the prime minister of Thailand, tried to buy a stake in Liverpool Football Club in 2004, angry fans waved banners reading: “Say no to Thai blood money”. The previous year, Thaksin had launched an anti-drugs campaign that had killed more than 2,600 people, many innocents among them. The Liverpool deal collapsed, and Thaksin – who, when pressed by journalists, could name only two Liverpool players – went back to his day job.

Then came the coup. Thaksin was overthrown by his own military in September 2006 and has spent much of his exile at a £4.5m mansion in Weybridge, Surrey. Here, he has achieved two notable things. First, he has spent £81.6m to buy Manchester City, a struggling football club whose grateful fans, unlike Liverpool’s, have embraced him. They call him “Frank”, because his family name looks a bit like Sinatra. “I really appreciate that you have accepted me,” he told supporters, before throwing them a street party in the city’s Albert Square, where he dished up free Thai noodles and sang the club anthem.

“Has anyone ever felt more optimistic about a new season?” one fan wrote in the Manchester Evening News, heralding the arrival of “Frank’s dosh”. (Thaksin gave Man City’s new manager, Sven-Göran Eriksson, £40m to spend on new players.) Suddenly, Thaksin’s violent past was either irrelevant or a positive advantage. “Mr Shinawatra was famous for cleaning up drug gangs and general low life in Thailand,” wrote a second supporter. “ManU fans beware. . .”

Which brings us to Thaksin’s second achievement in exile: with Man City’s help, he has recast himself as a wounded hero of democracy. “I was a democratically elected leader ousted by military coup, so I know the British people, as a mature democracy, understand my position well,” he said in August. “I am still very popular in Thailand and the military are trying to justify why they have overthrown me. There is no evidence that I violated human rights.”

The facts speak otherwise. Thaksin led a party called Thai Rak Thai (Thais Love Thais), yet more of his compatriots perished under his rule than under any other democratically elected Thai government. While twice elected to office by landslide majorities, thanks largely to his popularity among Thailand’s rural poor, he is no democrat. During its five years in office, his government stifled the media, intimidated political opponents and dismantled independent watchdogs monitoring his authoritarianism. People in southern Thailand blame his policies for sparking a continuing conflict between Buddhists and Muslims that has now killed more than 2,700 people. For millions of Thais, Thaksin is not the military’s victim but its facilitator: the man whose violent and scandal-plagued rule gave an unpopular military the pretext to seize power. Thaksin demolished Thai democracy; the tanks rolled in over its ruins.

Those scandals have pursued him to leafy Weybridge. In August, Thailand’s supreme court issued arrest warrants for Thaksin and his wife, Pojaman, over graft charges linked to a £12m land deal. Three weeks later, another Thai court issued a second set of arrest warrants in relation to their alleged violation of stock-trading laws. The couple have denied all the charges. Also in August, the New York-based group Human Rights Watch branded him “a human rights abuser of the worst kind” and asked the Premier League how he had managed to pass its “fit and proper person” test. “He’s giving himself some respectability in exile,” says Chris Baker, the co-author of a biography of Thaksin. “It’s also a way of keeping himself in the public eye. I don’t think he cares very much about football.”

While Thaksin serenades Man City fans, 6,000 miles away bereaved families too fearful to speak out while he was in power now seek justice for their innocent loved ones. Thai investigators have reopened dozens of drug-war killings, while a new independent committee is scrutinising how Thaksin’s government implemented such a murderous policy. Officials from both the Office of the Narcotics Control Board – the government’s main anti-drugs body – and the National Human Rights Commission (NHRC) now claim that more than 1,000 drug-war victims are innocent of all charges.

Thaksin has blamed the deaths on inter-gang warfare. “It’s a matter of bad guys killing bad guys,” he once said. In fact, all fingers point to his long-time employer: the Royal Thai Police. An investigation by The Sunday Times Magazine reveals how Thaksin’s policy unleashed police death squads across Thailand. It also illuminates one of the murkiest chapters of his rule.

“If you want to be a good leader,” Thaksin once said, “you have to be a master at storytelling.” His upbringing in the northern city of Chiang Mai taught him about “the hardship of poverty”, or so the master storyteller claims. His great-grandfather was a Chinese migrant who arrived in what was then Siam in the 19th century and married a local woman; the family later took the Thai surname Shinawatra, meaning “does good routinely”. By the time of Thaksin’s birth in 1949, the silk business had made the Shinawatra clan rich and influential. His father was an MP whose businesses included two cinemas and a BMW dealership, and Thaksin attended an expensive private school.

After a two-year spell at cadet school, he entered police academy. He graduated top of his class. and in 1976 married Pojaman, the daughter of a high-ranking Bangkok policeman. He later received a master’s and a doctorate in criminal justice at universities in Kentucky and Texas.

By the time Thaksin left the force in 1987, he was already running a failing business, leasing computers to the police, and was deeply in debt. But a spell as a politician’s bagman, which involved paying off MPs with cash, had taught him that “money was becoming a major factor in politics”. Soon, by exploiting his connections, Thaksin had secured government concessions in highly lucrative telecoms businesses. Thailand’s booming economy boosted the value of his companies, and in 2001 he first appeared on the Forbes rich list, with an estimated worth of $1.2 billion. He channelled part of this enormous wealth into his new political party, Thais Love Thais, and was swept into office in 2001.

Populist schemes such as cheap healthcare guaranteed his re-election four years later. So long as their economy prospered, most Thais were willing to overlook Thaksin’s autocratic style. His downfall began in early 2006, when his family sold its shares in Shin Corp, the telecoms giant he founded, for a cool $1.9 billion to the Singaporean government. Urban Thais accused the family of avoiding tax and selling a national asset to a foreign country, and street demonstrations swelled. Then the tanks rolled in. Thaksin was in New York, preparing to address the United Nations, when his own generals seized power in Bangkok. Fearing for his safety, he has never returned to Thailand.