>>>I don't believe there was an arrest warrant at the time, so the most the 'authorities' knew was that he was a suspect; albeit pretty much a slam dunk. We haven't seen (and probably never will) exactly what the captain was told - actually, informed about since there was no voice comm involved AIUI.
You make a good point, and I also wonder what was said per ACARS. Scary Mary aside, there's something to be said as far as continuing have been a calulated risk. If they had turned back to EWR (irrespective of the reason announced) might the perp have suspected something was up and taken some other action? The police's assertion that he was suicidal could have been assessed as an assumption--and that the gent's earlier plan had been superceded, as evidenced by the trip back to India. That's certainly not the only interpretation possible, but like you said, we'll probably never know the details.
As a dispatcher, I'd have given him the full scoop (sans any management filtering) and discussed options with him, as I'm sure COA's dispatcher did. There's always an economic consideration involved somewhere (and fuel ain't cheap these days), but my hunch is that the collective decision was to let sleeping dogs stay asleep, and nab him without risking the other pax once he deplaned.
I also think the much of the PHX LEO's frustration was self-induced, namely assuming one airline employee is interchangeable with any other, and that everyone knows everything and anyone can do anything. US FAR Part 121 airlines have these things called "Dispatch Offices" and the operational control emanates from there. You can really blame the LEO though--an FAA inspector didn't realize it either some years ago when he tried to stop that NWA flight from departing FAR-MSP with the crew he suspected as being intoxicated.