The cop who wasn't there

So, let me see whether I've got this right.  According to Yau Nai-keung – Assistant District Commander of Crime Yuen Long - the police were called to the scene of a possible crime, but hung around for 2.5 hours waiting for all evidence of the crime to be erased before they actually went in to check it out.  This seems a distinctly odd method of policing - in fact, its sheer absurdity reminded me of Major Major in Catch-22, who only sees people in his office when he's not in his office.