because shes bellatrix lestrange and she works for voldemort and is evil.
Sirius Black was murdered by his cousin, Bellatrix Lestrange, because she is the crazy, murderous type. He wasn't on Voldemort's side and Bellatrix was one of Voldemort's loyal servants.
Draco is Sirius's 1st cousin once removed.
Sirius Black (Harry Potter's Godfather) was murdered by bellatrix lestrange, Sirius's Oldest Cousin.
Bellatrix is very pro pure-bloods and Sirius who is against that was not seen as a cousin to her but as someone on the other side who she would be happy to kill - in fact because he was related to her she wanted the 'pleasure' of killing him herself.
Harry potter has a godfather and his name is sirius black
Sirius Black. His cousin Bellatrix Lestrange killed him
Sirius Black, Harry Potter's godfather, dies in Harry Potter and the Order of the Phoenix by Bellatrix Lestrange, his cousin, in the Department of Mysteries at the Ministry of Magic.
The producers didn't make the decision to kill Sirius. The films are based on books and it was written in the books by J.K. Rowling to kill him. Sirius was killed because it made Harry lose yet another parent figure in his life and that affected him throughout the rest of the stories.
Sirius Black was killed by his cousin Bellatrix Lestrange.
Voldemort did kill James and Lily Potter, but it was Bellatrix who killed Sirius Black.
Sirius Black was killed by his cousin Bellatrix Lestrange during the Battle of the Department of Mysteries.
Bellatrix Lestrange was the one who killed Sirius Black in the battle of the Death Eater's and the Order of the Phoenix in the Ministry of Magic.