If I'll want to evacuate the plane this is what i'll do,this is cpt's decision everywhere I've been.
I don't think the info regarding police ordering them not to evecuate is accurate.
You should also know that most of the times the evacuation should not be rushed,due to potential injuries to the pax during this manouvre.If the stairs will be at the plane in the next minute or so,maybe you'll decide to wait a little bit before opening the slides ..
About local police entering and doing whatever they want on board of a foreign airplane,I very much doubt that...