Here's what really happened:
* Peter Pettigrew (Wormtail), a close friend of James and Lily Potter, betrayed them to Lord Voldemort.
* Voldemort murdered James and Lily, but Harry survived because of his mother's sacrifice and the power of love.
* Sirius Black was wrongly accused of betraying the Potters and was imprisoned in Azkaban for twelve years.
* Pettigrew faked his own death and became Voldemort's loyal servant.
The truth about Sirius Black and his innocence is revealed in Harry Potter and the Prisoner of Azkaban.