People in the Creepypasta fandom have saved the old Sesseur’s YouTube account on web.archive.org. Here is the proof that Sesseur (@killerjeff) posted a video about Jeff The Killer's story on October 3, 2008:

https://web.archive.org/web/20130217065913/http://www.youtube.com/watch?v=l4ZL-57j7fo

I described it in more detail in my post on DeviantArt, there are more links:

https://www.deviantart.com/stasythekiller/art/For-all-Jeff-The-Killer-fans-871867621

Reuploading the same video with the same song (The Posies «I Guess You’re Right») that was playing in the original video:

https://m.vk.com/wall-171003625_315

And reuploading of video on Sesseur’s new YouTube channel:

https://m.youtube.com/watch?v=p7Jp2NAph7s