COSTELLO: Police in Colorado are on high alert this morning after a chilling call to 911. The anonymous caller targeting officers in Aurora and Denver.</s>UNIDENTIFIED MALE: We are about to start striking fear shooting down all the cops that we see by their selves. This will go for the sheriff's department. You guys are evicting innocent people. Let us catch you by yourself and it's shots fired.</s>COSTELLO: Chilling, right? The head of the Aurora Police Association says officers will ride in pairs in patrol cars to help ensure their safety. It's back to work for the man who killed Cecil the lion. Just over an hour ago and without much uproar the Minnesota dentist Walter Palmer walked back into his practice. For months the dentist and big game hunter has found himself on the other end of the hunt becoming a target of protests and death threats. Boris Sanchez joins me now. He's following the story. Good morning.</s>BORIS SANCHEZ, CNN CORRESPONDENT: Good morning, Carol. A relatively smooth greeting for Dr. Walter Palmer as he walked into his office. Only a handful of protesters out there. Some of them you might have heard chanting extradite Palmer very different from what we saw that last week of July when his office had to be shut down after there were so many protesters outside. Very aggressive and very angry.
Cecil the Lion Killer Receives Threat.