Shuttle Columbia downed by others means?

The official story of the Space Shuttle Columbia disaster is that the shuttle went down because of damage caused at its launch when a peace of frozen foam came of Columbia's external tank. But recently another belief is that the shuttle was brought down by an unknown craft. I was very unbelieving of course when some one described the craft until I saw a news clip from Fox News Channel of the craft that was described brought down Columbia on the news clip. I was stunned and now lean to the side that Columbia was brought down by an unknown craft on it's way back to earth.