Neopagans and others say that St. Cyril of Alexandria was a criminal. The pagan Damascius(ca. 480-550 A.D.)was the first to make this accusation. He wrote about a century after the gentile philosopher Hypatia of Alexandria was murdered by the Christian mob in 415 A.D. Although he lived much later than the event, he speculates that St. Cyril secretly became envious of her and ordered her murder.
St. Cyril wouldn't gain anything from her murder. She wasn't a faithful pagan and she didn't do anything against him. She also had a number of Christian students, one of which was bishop Synesius the Cyrenian. It is said that she once wrote to him "I long to die as a Christian"(source: π. Γεωργίου Μεταλληνού, Παγανιστικός Ελληνισμός ή Ελληνορθοδοξία; Αρμός editions 2003). It is possible, though, that she was the political advisor of the governor Orestes, an enemy of St. Cyril. This isn't a real motive for St. Cyril to kill her, since such a thing would only arouse Orestes' anger. St. Cyril did have power, but he could be punished.
Hypatia was murdered by a mob of fanatic Alexandrians who thought she was the reason for the rivalry between St. Cyril and Orestes(Socrates Ecclesiastical History 7.15 and John of Nikiu Chronicon 84. 87-103). The murderers weren't the "parabolani", the patriarch's guard. The people of Alexandria were famous for their riots(Socrates Ecclesiastical History 7.7 and St. Cyril Homily for Easter, 419). Socrates Scholasticus(ca. 380-450 A.D.) says that the one who urged the mob to kill Hypatia was a reader named Peter, and not St. Cyril. A reader in Alexandria wasn't nessecarily a baptised Christian(Socrates Ecclesiastical History 5.22).
Maybe someone will say that Socrates admits St. Cyril's guilt since he says that "the murder of Hypatia brought not little disgrace on Cyril and the Alexandrian Church". This doesn't mean St. Cyril ordered her murder!He was simply embarassed by his flock.
Socrates isn't lying in favour of St. Cyril, since in other places of his work he disagrees with the latter(Socrates Ecclesiastical History 7.7 and 7.14).
The evidence that we have is favourable towards St. Cyril's innocence. What is certain though is that any kind of murder has nothing to do with Christianity. And we should always remember that people aren't born as saints. They become saints. Even if St. Cyril was involved inthis murder, he later repented and became a saint. Many of our saints were tremendous sinners before they abondoned their previous life and devoted themselves to our Lord.