The United Nations General Assembly was not in session. Their headquarters were closed, and surrounded by lookout posts of NYPD and US National Guard. The access to UN site was protected by barricades, and heavy dump trucks loaded with gravel. From the East River side the UN site was also protected  at all times by at least one US Coast Guard patrol vessel. There were also NYPD police cruisers on constant tour of duty on both ends of a tunnel where FDR highway runs under UN buildings.