And after videos. Assuming it is correct, I didn't get other sources, there was a big jump in time with Bolt from 2007 from when he lost some races then started winning with crazy fast times in 2008. His physique also became more bulky before big races like the Olympics. He improved by .6 seconds in one year. This is basically inpossible without drugs.

I am surprised his career was never ended by injuries.

Here is the Quora, it is the second answer, so you have to scroll down. There are some videos and explanation given, interesting read.

https://www.quora.com/Is-Usain-Bolt-doping