As I said, in some countries, you can't treat an on duty public/government "servant" like that.
Most people, even mayors, make appointments when they formally visit another organization in an official capacity. They don't just walk in and expect to be seen.
Which means he'd have to have a warrant. If an Officer was "just investigating", they have to be invited or have a court order to get onto private property.
In America anyway.
Otherwise, yes, a police investigator needs permission, or a warrant, to go onto the Apple campus and ask questions or look around.
I'd be rightly ticked off if someone did that to me, and I'm not one of the worlds richest and most secretive companies.