Jd please read post 141 I do hear what you are saying but a lot of these incidents start with Joe average citizen calling because they are paranoid that everyone is a terrorist--why they are that way is another topic. So when you as Joe citizen call the police to report something that you think needs looking into and the police stay at the station because no crime has been committed yet--thats OK?? You would expect them to investigate--ask questions. Like they did in david b incident.
I have read the comments between 23mjm and several other posters with interest. 23mjm, while I respect and PARTIALLY agree with your point that good police work involves investigation on tips from the public. LE cannot be everywhere. While I believe the public should be vigilant, I think too they have been "over-amped" with a fear campaign, but that is another topic. I want to focus of this post to be on "good" police work.
I was an active duty police officer very early in my working career, and a key investigative tool in our training was the skill of observation before intervention. Therefore, no one here is suggesting that LE should not respond to public tips by staying in the station. The real issue is how they respond.
We were taught to respond and observe the situation before deciding to intervene - ESPECIALLY when the situation was innocuous. Before I receive a flurry of posts suggesting inactivity, this is not the case. If we responded to a public call that someone was trying to break into a car (even if it turned out to the owner), we would immediately intervene. Or if two individuals were in a wrestling match that could have turned out to be friendly, there would be immediate intervention after virtually instantaneous observation and assessment of the situation. As a civilian, I was changing a tire, in the dark, late at night when I was checked by an officer. He wanted to be sure I was ok. As I was on the side of a public thoroughfare and although I was not doing anything illegal, his observation would have then switched to assistance mode and he was justified to verify my well-being. Again, good police work and public service.
The sight of someone taking photographs would not justify a direct intervention unless that person had his tripod set up in a hazardous location (like in the middle of the street) or on private property. The notion that public buildings are somehow "targets" is absurd given the previously posted sources of photographs available extensively throughout the web. As a police officer, observe certainly, but go up and harass him/her with questions? No, that is intrusive.
If this is permitted for photography, where will it end? The OP is standing in the same place sketching a street scene (as an artist) and gets hassled? Or the OP is hassled for filling in notes in his daytimer, at that same place, as he happened to have a creative thought about some business problem totally unrelated. This is a slippery slope where potentially the act of 3 people standing together conversing becomes a suspicious assembly. Welcome to Germany in the late 1930s!
Back to the point about good police work. Contrast the hassle I received (as outlined in a previous posting by me) for photographing NOTHING of national security importance. Two police officers harassing me on a public street corner, questioning what I was doing and still demanding ID after I provided a completely plausible, polite reply, and then running my ID through the car computer when I complied (for expediency).
Then, on a completely different occasion, I am a mile or so outside a nearby town waiting to photograph a steam train due to go by on a single set of rail tracks. No one is around me for several miles/kms. My car is safely parked off the road on an approach to a farmers field. My tripod is set-up in the ditch well off the gravel road and the rail tracks with my MF RB67 on it, awaiting the steam train. During that time, someone must have called me in, as a local police car from that nearly town (I still know the car codes) comes up and stops about 1/2 mile away from me. She watched me for a bit, then she drives by on the road, has a quick look at what I am doing, and then drives off. THAT is GOOD police work. There was NO REASON for her to stop and question me. THAT is what should have happened to the OP - not getting rousted with intrusive questions by the FBI. If I had been on the rail tracks that day, then I was a trespasser and a hazard on private property and THAT would justify a full LE intervention.
I remain convinced that our freedoms are being eroded by sloppy and intrusive police work encouraged by draconian legislation changes driven by keeping an ignorant public amped up with unnecessary fear. Unfortunately, we photographers, by virtue of the curse of the visibility of our tripods, are an EASY and ACCESSIBLE first-order target for this type of harassment and intrusion. We should be Ghandi-like in our non-violent resistance to this unwarranted harassment when engaging in a perfectly legal pursuit in a so-called "free" society.