We weren't told why the police were arriving. After they had let everyone off and were continuing on to Hamilton we were told: "I apologize for the delay; there was a security issue that needed to be addressed. Thank you for your patience." At the time, I figured it was an unruly customer who'd taken a swing at one of the ticket collectors. (There are signs up saying that assault on train personnelle performing their duties is punishable by up to 5 years in prison) Annoying, but I'm willing to put up with some delays if it's necessary to ensure that people aren't fighting on the train.
So what was this security issue? Two guys with a video camera were filming the inside of the train. It turns out that the two men were journalists from Hong Kong. Apparently they were working on a documentary about a Hong Kong engineer who had designed part of the new train cars. (And these new double-decker cars are nice)
Despite the title of this post, I've been thinking as I write this if after all the situation was handled appropriately. I mean, yes, the police taking anyone away for questioning (even if the people went "voluntarily") after a legal activity bothers me; so far as I know, the US has not yet implemented Soviet-style prohibitions on taking pictures inside moving vehicles, so I'm bothered by that. On the other hand, the two men weren't held overnight, I can see how videotaping various structural components of the train could be suspicious, and then there's the matter that yesterday was Tuesday, September 11th. (One wonders why the two men didn't start by contacting NJTransit's PR department)
So maybe the actions of NJTransit were appropriate, if a bit frustrating to commuters. For the record, my arrival in Trenton was delayed only a bit over 15 minutes (certainly less than the 20 quoted in that post). I've been delayed longer from wet tracks.
What definitely wasn't appropriate though were the multiple calls to 911 mentioned in that post from commuters stuck on the train wanting to know where the police were. Being 20 minutes late getting home isn't an emergency.