Reports of Explosions and Explosive Devices on 9/11

There are many reports of explosions on 9/11, you have probably seen the footage showing the small explosions along the length of the towers just prior to the buildings coming down. Have you seen the footage of the police reporting explosive devices being found and even evacuating people due to the discovery of explosive devices? Why would they do this?

Check out the video below, specifically from 3m51s

BBC News announce the collapse of WTC building 7

This broadcast was made at 4.57pm (Eastern Time), the report is clear about the collapse of the building...only trouble is that the building did not 'collapse' until 5.20pm (Eastern Time).

The presenter as with most of the presenters you see on the news are reporting what they are told to report. Why would they have been fed this line before it even happened?