Completed items kept within the Project?

I would like to see the items/tasks under the project even though I have them marked as completed. How can I do that by project and not by date?

Try making this perspective:

Don’t use Project Hierarchy
Group actions by Project
Sort actions by Project
Filter by status - any status
Filter by availability - Completed
Any duration
All contents

You could also simply click on the View button in the toolbar and choose to show all items instead of remaining.