Beleduc - XXL Puzzle - Detective

Who has ever been like a detective and gone out on a search? This puzzle makes it easy to find things out, to discover, to look closely and to search. The red plexiglass screen in the middle can be removed and placed on the areas that at first appear red and “opaque”. Take a close look and see what you can observe!! Also, the margin is full of symbols. Can you find all of them on the puzzle?