But suspicous and illegal are fsar different. I had experienced something similar while doing some video work for a documentary about the VCU French Film Festival (one of the largest in the world outside France). A function took place at the Virginia Museum and I had to argue my way in. The guards said it was against policy and required the museums permission. I explained that I was part of the function and documenting that function was my job. Eventually they relented but I had a permanent "shadow" for the evening.
In the fall I wanted to shoot some of the museums buildings, which include a chapel built for Civil War Veterans in the 1880's. This time I called the museum, spoke with the head of security, told him about the issues in the Spring and was assured that I was completely within my rights to photograph public buildings. But the head of security is a far cry from one of the guards.
Interestingly enough I was at the museum last weekend for the last day of a Latin American Exhibit from the permanent collection. I spent over an hour looking at six Bravo's, one Rivera and 3 Orozco's. After 30 minutes I again had a shadow for the rest of the time. I think that bending over and looking up at the Bravo's to check for spotting must've been suspicious.