Hmmmm.... I could be wrong.... the way I saw it is that the assasin is further down the steps from Michael and to the left (of the steps as you're facing them). He takes aim at Michael, but Mary comes storming up to him to find out why he's ruined things for her and Vincent. The shot is fired, Michael ducks (or perhaps he dives becuase the bullet skims his arm I think) and the bullet meant for him hits his daughter....who was confronting him for interfering in her life.....doubly tragic. Anyway, it's all a bit JFK, but the trajectory of the bullet seemed to be right. Could be wrong of course.

...there's people who would pay a lot of money for that information. But then your daughter would lose a father..instead of gaining a husband.