The author of this art is unknown. According to one of the managers the artist behind this creation didn't want to reveal his name or info about his life. Therefore at the debut of the statue he was dubbed as "unknown author".

 Many theories arrised about them. Some say that he was a criminal who stole the art piece from someone else. Some say that the reason why people hear screeching is because it's thousands of souls were trapped by that person ,so he could have "special" statue that will be easily accepted in the museum.

 It's speculated.

only speculated