I need help getting the catch skull- Halo 3

Hi. I know were the catch skull is, its on the top of that round building in the first open battle on the storm but every time i get up there, its not there. i start from the beginning of the level and no wraiths are destroyed when i get up there.. Whats my problem?

That doesn't make sense... it should be on that Silo on the right side of the field. If you haven't destroyed any Wraiths, it should be up there... you need to jump on a Warthog or something to get up there but if you're up there, you know that already. The only other reason it wouldn't be up there is if you were playing on easy. Maybe an explosion knocked it off???

Thats just weird.