-At season 5, after Gogol explains his plan for killing Dostoevsky, we go into Sigma's thinking and memories.
-He speaks of his own backstory and explains it in the right details
-Gogol drags him to the fucking store to buy some heels
One thing that I can understand for the terrible backstory explanation is that because it was Fyodor that was telling it, so he may not have known about all the details of him being used for evil, therefore Bones was SAVING the full story for season 5 :)))