The "evidence" is that he ran faster???? So by using this as evidence, everyone who runs faster thoughout their career is a doper?? Or, are we back to the "if you ever tested positive, any performance thereafter - but only if faster - is evidence of doping"??? Or, are you saying the benefits of doping last over 6 years?
I don't know with absolute certainty Gatlin isn't or hasn't recently doped, but it's going to take more than the typical LRC rant or weak logic to make a compelling case. You can't prove a negative, but that won't stop the whiners whining - if only the "beyond reproach" Nick Willis could run the 100 we'd have a clean race. But wait, at 31 he just set his personal best - must be doping?? But wait, that's a really stupid argument....
"Evidence" is some fact that tends to make a proposition more or less likely. Something doesn't have to be conclusive in order to be evidence; and the existence of some evidence in support of a proposition doesn't mean that the proposition is necessarily true.
Nothing in the life is absolutely certain - we look at the evidence for and against and make an assessment based on that. One question is how certain we want to before reaching a conclusion. Lawyers make a distinction between the civil of proof - balance of probabilities; and the criminal one - beyond reasonable doubt.
Given Gatlin's previous positive tests; apparent lack of genuine contrition and his current performances there's certainly a good chance he's doping. But we don't know for sure.
Of course there is a chance that any athlete is doping. But we at least like to give those who have never tested positive the benefit of the doubt.
At best you can assert suspicion, but I've not seen this case being made.
As to legal standards, what you assert past positive test(s) (actually one - see http://www.usada.org/wp-content/uploads/AAA-CAS-Decision-Justin-Gatlin-January-2008.pdf page two where USADA basically says first wouldn't have been a positive but for failure to properly/timely file paperwork ), lack of genuine contrition (very weak in terms of being dispositive, even if it's assumed for the sake of argument) and current performance (can raise suspicion but if he's passing his tests good luck with this in a court of law) - is extremely weak.
You can be suspicious and want him to be guilty, but I've yet to see anything be asserted with solid evidence (your post supports suspicion NOTHING more) that approaches probability let alone proof beyond a reasonable doubt. But of course this is LRC, everything is subject to suspicion and all accused are guilty. Critical thinking and due process are tough and don't provide the immediate satisfaction of smug self-righteousness and compensation, via vicariously "participating" in T&F, for feelings of inferiority.