Who is responsible when a self-driving car kills someone?

Early Monday morning, an Uber-owned Volvo in autonomous mode struck and killed a pedestrian. The vehicle had a human driver behind the wheel when the tragedy occurred. 
This incident brings a sudden urgency to the moral quandary that ethicists have been discussing since before self-driving cars were a reality: Whose fault was this death? 
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This is believed to be the first time a self-driving car has caused an accide