Why does the gov lie , when the truth would work just fine?

Today the gov changed its story. Now, Osama was NOT armed, and he did NOT use a woman as a human shield, and the 'mansion' he was living in, looked more like a Memphis slum than a luxurious home. At the same time one of Osama's daughters is claiming that we captured him, and them shot him to death in front of her and other family members.(which i assume is a lie, but it does not look good when our own story was obviously B.S.)