What law limits freedom of speech in the Capital building? And what did Cindy Sheehan's T-shirt say?

Better to ask: Is there a law that limits speakers to telling the truth? or at least names lying as an punishable offense? W can falsely assert the following without consequence but Cindy is arrested for wearing a T-shirt that says: 2,245 Dead — How Many More?? 

". . . It is said that prior to the attacks of September the 11th, our government failed to connect the dots of the conspiracy. We now know that two of the hijackers in the United States placed telephone calls to al Qaeda operatives overseas. But we did not know about their plans until it was too late. So to prevent another attack –- based on authority given to me by the Constitution and by statute -- I have authorized a terrorist surveillance program to aggressively pursue the international communications of suspected al Qaeda operatives and affiliates to and from America. Previous Presidents have used the same constitutional authority I have, and federal courts have approved the use of that authority. Appropriate members of Congress have been kept informed. The terrorist surveillance program has helped prevent terrorist attacks. It remains essential to the security of America. If there are people inside our country who are talking with al Qaeda, we want to know about it, because we will not sit back and wait to be hit again." 

Let me break it down: 

1. It is said - By whom? 

2.