I'll Take Your Film!

So I just started working for a small paper and I was about to shoot a bb game when I saw four unmarked SUV's heading down the street. I decided to follow them until they stopped a few blocks down. Once I parked my car and rounded the corner I saw three plain clothed officers go to a back of ahome and four or five more knock on a door and yell, "US Marshals, open up!" (I had it confirmed from a local patrolman that they were looking for a county inmate that was released by mistake.)

As the officers were about to get back into the SUV's I lifted my camera and one said to me who are you. I identified myself and he then said, "If you shoot any photos of us I'm taking your film!" I then asked who he was and he replied "US Marshals!" Since they didn't find the guy and I couldnt get near the house in time for a good shot, I decided against taking any photos.

Anyhow, I'm pretty good at Photography law, but it just caught me by suprise. I'm assumung that since I was on a public sidewalk he would have no right to take my film(card)?

My question is: If he would have tryed to take the film what could I have done and did anyone ever come accross this kind of situation? I mean I guess I could have said where's your warrent?

D.