And exactly how does one adjudicate whether or not the officer had probable cause?
Probable cause for arrest - a fair probability that a crime was committed and a fair probability that the suspect committed that crime.
Definitions of Probable Cause on the Web:
a reasonable belief that a crime has or is being committed and is the basis for all lawful searches and arrests
the reasonable belief that a person has committed a crime.
http://faculty.ncwc.edu/toconnor/315/315lect06.htm
I. Direct Sources of Probable Cause (Officer sources of knowledge)
FLIGHT : Attempting to flee, evade or elude, is in evidence law a presumption of guilt.
FURTIVE MOVEMENTS : "Furtive" means secretive or concealing, and the law requires a totality of circumstances here. The movement cannot possibly be construed as an innocent gesture (looking both ways before crossing the street). Nervousness alone is not sufficient as the law recognizes the right of people to be nervous or fearful around police. The movement cannot also be possibly the sign of a mental condition. There must be something secretive given the time, setting, weather, and audience. It would be best if the furtive movements were identifiable with a particular type of crime.
OBSERVATION OF REAL EVIDENCE : "Real" evidence is demonstrative evidence (Exhibit A) that speaks for itself. ADMITTED OWNERSHIP : This involves, for example, a type of consent in which a person, say, accidentally empties the contents of their purse or pockets, and the police ask them if they own something, and they say "yes", and then the police look inside it and find contraband, they are said to have had probable cause for the search and seizure.
FALSE OR IMPROBABLE ANSWERS : This is not normally a basis of probable cause alone, but it tends to trigger subsequent police inquiry or action. Examples might include a person being asked who the car belongs to, and they say "my cousin" but they don't know their cousin's name. Or, a girlfriend answers the door and says the apartment is rented under her boyfriend's name, but she doesn't know what kind of car her boyfriend drives.
PRESENCE AT A CRIME SCENE or IN A HIGH-CRIME AREA
ASSOCIATION WITH KNOWN CRIMINALS
PAST CRIMINAL CONDUCT
FAILURE TO PROTEST