World Trade Center Building 7 wasn't hit by an airliner like World Trade Center Buildings 1 and 2 were and it was a block away from World Trade Center Building 1, which was the nearest of the two "World Trade Center Twin Towers" or just over a football field away with another building in between.

World Trade Center Building 7 received only minor damage to one corner from the falling debris of World Trade Center Building 1 and had only isolated pockets of fire that moved from place to place as office furnishing fuel was consumed, but still imploded at 5:20 PM on September 11, 2001 and accelerated toward the ground at free-fall acceleration, around 8 hours after World Trade Center Building 1 and 2 had collapsed.

The NYPD officer is tell the people to move back away from World Trade Center Building 7 because evidently they got word that the building was about to explode.

{jwplayer}&file=http://www.youtube.com/watch?v=http://youtu.be/cU_43SwWD9A&type=youtube&title="9/11 CNN NYPD WTC7 - The Building Is About To Blow Up (RAW)"&image=http://www.911tap.org/images/site/evidence/videos/videos-by-others/law-enforcement/img/911-cnn-nypd-wtc7-building-about-to-blow-up-poster-img.jpg{/jwplayer}