If police are present while you murder is it not a crime?

NO! It is still a crime. Period. Think about this:
There is a riot. Police are everywhere. You shoot someone during the riot, with a cop standing next to you. You STILL murdered them and are guilty of murder. It doesn't matter that the cop was standing next to you.
Untrue.

The presence of police do not change the nature of the action, and do not make it any less of a crime than it would have been if there are no police present.
Still a crime

Now you just have witnesses with high credibility and no place to run.
Are you nuts?


Answers:
murder is murder.what is your point?
That's even worse, now the police are witnesses to your crime. Let's hope they're not accessories!
Murder is murder no matter who is present.