WHY WERE THE HELMET NUMBERS HIDDEN?

At Ankara the helmet numbers of police officers who intervened to protests was erased
During the protests at Ankara, the violent intervention of the police is criticized. As seen on television and taken photographs, the police officers had hidden their helmet number with a sticker or a marker pen. That image has raised strong reactions. The question is the following: why the police erased those numbers? These numbers are the sole traces to identify a police officer in case of illegal intervention. A response from concerned authorities is expected.