Why has the pentagon footage of 9-11 never been given to the public?

The Pentagon has cameras everywhere. The explosion at the pentagon on 9-11 has been shown, but they [the US gov] start the footage just after the impact. We never see exactly what hit the Pentagon. They could show us exactly what hit the pentagon, but they don't. Why doesn't the gov show us what hit the Pentagon? Don't we have the right to know?