The case against Clemens came down to his trainer, Brian McNamee.
McNamee was the prosecution's key witness, and if he was believed then Clemens would have been in trouble. The issue for the prosecution, though, was that McNamee failed as a witness.
There were two problems: McNamee's credibility and the integrity of his Clemens DNA samples.
First, McNamee did not come off as terribly credible on cross-examination. The jurors probably had a tough time believing him. He cut a deal with the Feds in exchange for his testimony - so he had in the eyes of the Clemens defence team the incentive to lie. As well, he had a bit of a rap sheet, including tax evasion and drug trafficking. His ex-wife, he was a composed and believable witness, didn't back up McNamee's story that she urged him to safe Clemens' DNA.
Second, McNamee testified that he had the DNA of Clemens preserved on syringes, pads and gauze. The problem is that he admitted that he stored the DNA in a Miller Lite can - and worse - along with the DNA of other players. The integrity of the DNA samples became a major issue. Given the way they were stored, could the samples be considered reliable? Were they contaminated?
The issues of credibility and DNA integrity were very likely key considerations for the jury. the prosecution must convince the jury that Clemens was guilty beyond a reasonable doubt. This is a high standard to meet. Before a jury is going to toss someone in jail, they want to be fairly certain the defendant is guilty. In this case, they could not find any such assurances.
Is it now proper to conclude that Clemens did not do PEDs? No. This was not a referendum as to whether Clemens did PEDs. This was a trial about whether Clemens lied about doing PEDs - or perjured himself when he said he didn't do PEDs. There is a slight distinction but an important distinction nonetheless.
For Clemens, the next significant moment will be the Hall of Fame vote and whether he gets in.
Ultimately, before the trial started, the prosecution had a decent case in some respects. However, things unravelled when its key witness, McNamee, took the stand. That's when things fell apart.
And that's why Clemens walked today.