Helicopter maneuvers

Today as I was walking past the MIT rowing pavilion I noticed a helicopter flying low over the Charles. I've see low-flying 'copters there before so I was not too surprised, but then as I approached the Harvard Bridge I noticed the police had closed it to pedestrian and car traffic. The helicopter circled three times from the rowing pavilion to the bridge and back and then took off, though I could still hear it nearby. The police then let the people and cars cross, but as I got to the intersection two officers took up posts on the sidewalk on either side of the bridge. No one was walking there at the time so I couldn't tell if pedestrian traffic was prohibited again. It seemed like if they hadn't already shut down the sidewalk they were going to do so soon.

The thing about our lunchtime observations is that we very rarely are able to find out why something happens. Instead we witness strange events that leave us confused. I'm assuming the helicopter maneuvers were planned since the state police seemed to be timing everything, but I have no idea why the 'copter was flying like that. Was it looking for something or someone? Inspecting the bridge? Practicing for an emergency? I suppose I could have asked the officers, however I would have felt weird, especially because I wasn't planning to cross the bridge so the sidewalk closure was of no relevance to me. This will have to be another one of those strange events we ponder for the rest of our lives. Or at least the rest of the day.