case against Bolt:
As you may know, since late 2009 (or beginning of 2010) the IAAF introduced the "biological passport" as the latest weapon against doping techniques:
Quoting Dr Gabriel Dollé, head of the anti-drug department at the IAAF:
"Athletes who use PED know that it disappears very quickly in the urine, If they are well prepared before a competition at PED, they keep dring the competition the benefits of increased red blood cells in the blood. PED having disappeared from the urine for a long time, we can make as much urine test as we want, we do not find anything. " To overcome the shortcomings of traditional anti-doping tests, "we must ensure strict monitoring throughout the year to see how their profile changed"
this method is not revolutionary stricto sensu, because it's not a direct detection method, but it allows to keep an eye on those who use PED throughout the year and refrain from using them once the competition approaches. It was introcuded in cyclism and immediately a bunch of cyclists were found with unstable parameters. it's also effective against new generations of PED and molecules who are always one step ahead the detection techniques; as a famous example the PED positive test of Lance Armstrong, 6 years after (in 2005 for samples of 1999!)
as for athletism: the "steroidian passport" part of the "biological passport" started just after the world championship in 2009:
my conclusion: the athletes (like Usain Bolt) whose performances dropped significantly in 2010 and 2011 are the most suspicious! Usain Bolt repeated several times that he won't do fast times like he used to do this year (he knew that before the season started) but he will be ready in 2012 (he may be caught in 2012 or may not be able to do a sub 9.8 again)..
as for Powell, well I think he's clean, stable performances, he did a 9.78 this year (he's28) which is understandable, although he's muscular, he's not bulky, doesn't have the swollen veins nor the red eye symptom