Agreed.
I keep seeing both sides of this though. Very stupid to put devices with menacing characters on them and wires hanging out on bridges and stuff...but when a cop discovers the first one and a foreign exchange student owns up it's a stunt for a TV show why don't the cops say take them all down immediately or go to jail, end of panic?
Once the cat is out of the bag, it is exceedingly difficult to get him back in.
It would have been better if the Boston Police did as you say, but it is not at all unforseeable that they would react as they did. They are a police department. Step One is to Protect Bystanders By Cordoning Off The Area. Step 52 is Stop And Think It Through.
The second you say "We're closing Highway 92", the immediate question is "Why?"