Doping: Armstrong was defiant until his 'best bro' finally spilt the beans

"Lance Armstrong doesn't want a hug," Floyd Landis famously told the writer Dan Coyle in 2004. "He just wants to kick everyone's ass."

For years, that is precisely what the American did as he amassed a record seven Tour de France titles, defying those who wrote him off following his diagnosis with testicular cancer and those charges of doping levelled by former team-mates, journalists such as David Walsh and the French sports daily L'Equipe.

But following a day of dramatic revelations that shredded Armstrong's reputation at a stroke, it appears there was one opponent he could not resist: the US Anti-Doping Agency and its tenacious chief executive, Travis T Tygart.

For somebody who has made his name and reputation by refusing to concede defeat, Armstrong's decision not to contest the latest doping charges against him will seem curious. It will also be interpreted by many as an admission of guilt, and so the question is why, and why now?

Unfortunately, a consequence of Armstrong's refusal to fight the USADA charges is that we may never know for sure. One theory is that the sheer weight of evidence against him made the task of clearing his name far more daunting than anything he ever faced in the Tour de France.

Many will suspect that the answer could lie in the testimony of one rider in particular; not the 10-plus former team-mates who have become sworn enemies - including Landis, Tyler Hamilton and Jonathan Vaughters - but George Hincapie. It was Hincapie who rode by Armstrong's side for all seven of his Tour wins. While other riders left and fell out with Armstrong, or tested positive for drugs, Hincapie was loyal to the end. Now 39, Hincapie recently finished his 17th Tour - a record, for which he was allowed to lead the peloton on to the Champs-Elysees. But midway through the Tour the New York Times claimed: "Hincapie has told the United States Anti-Doping Agency about systematic doping on Armstrong's teams, [in] which Armstrong played a part."

The respect between Hincapie and Armstrong remains, with Armstrong describing him as "his best bro' in the peloton". It is this that makes Hincapie's evidence potentially so devastating. While Armstrong has been able to dismiss others as bitter has-beens or never-weres, he could not so easily distance himself from the sworn testimony of his "best bro".

There is nothing new in the allegations around Armstrong. Although one of his most-repeated lines of defence is that he has never tested positive, this is not true. He tested positive for corticosteroids during the 1999 Tour, but produced a backdated doctor's prescription and avoided a sanction. Six years later, L'Equipe claimed retrospective testing revealed the presence of EPO in six of his urine samples from 1999, though the case was dismissed.

In the first couple of years of his Tour-winning run Armstrong was seen as a redemptive figure. Cycling needed a hero after the 1998 Festina scandal, which exposed systematic doping on a grand scale.

Armstrong, the cancer survivor, became the symbol of a new era, on the basis, largely, of an implicit understanding that someone who had almost lost his life would not take drugs. But over the years the suspicion grew, especially when Walsh discovered that he was working with an Italian doctor, Michele Ferrari, who had been suspected of doping riders since the early 1990s. Ferrari has also been accused by the USADA and, like Armstrong, opted not to contest the charges.

By 2005, the suspicion around Armstrong was such that his retirement, following his seventh Tour, was welcomed by many. It heralded another fresh start. But two events, both involving Landis, have perhaps proved his undoing. The first was Landis's positive test while winning the 2006 Tour, which cast him into the wilderness. The second was Armstrong's comeback in 2009. By now the exiled Landis, who had been close to Armstrong when they were teammates, had become a thorn in the side of the sport, and of Armstrong.

He tried to launch his own comeback with Armstrong's new team in 2010, but was rejected. And a few months later he accused Armstrong of doping in 2002 and 2003, and alleged that cycling's governing body, the UCI, accepted a bribe from Armstrong to cover up a positive test for EPO in 2002, an allegation which the UCI has always strenuously denied.

More allegations followed from other former team-mates, including Hamilton. Federal investigators began to take notice; they were concerned that Armstrong's team, US Postal, had been funded by government money. The crimes investigated by federal prosecutors included defrauding the government, drug trafficking, money laundering and conspiracy, but in early February 2012 the investigation was abruptly stopped. That was when Tygart and USADA came in.

Tygart noted that his job "is to protect clean sport rather than enforce specific criminal laws" and launched an investigation into alleged doping. Tygart has insisted that sealed grand jury testimony formed no part of his investigation, but through leaks and third parties the identity of the witnesses, and what they had said, had become widely known.

It remains unclear how, or if, witnesses were persuaded to repeat their allegations to USADA, though most assume that, somehow, Tygart and USADA ended up with much the same evidence as was heard by federal agents in the course of their investigation.

With Armstrong opting not to have the case heard, we may never find out all the details, or the identity of the witnesses, though a book, Hamilton's The Secret Race, written in collaboration with Coyle, promises to tell all when it is published in September. It is likely not to be the only one.