When a Tesla on Autopilot kills someone, who is responsible?

In the US it could be decided by Congress by tomorrow but it won't, because legislators are feckless cowards. So it will be adjudicated up to the Supreme Court level sometime in 2032 or so.

That will have been some narrow case that barely applies anywhere with a middle-aged person no one cares about. A few states starting with California will then require some kind of Lidar-controlled cowcatcher-type solution.

There will be a different case brought to the Court in say 2040, when they are finally challenged to do something serious after a photogenic 5 year old is killed due to some provable negligence in Tesla's (or whoever's) software practices.

Around then there may be perhaps two Justices who understand the tech, but the rest won't. The Court will mandate something even more idiotic or will simply kick the case back to lower court.

By then it will no longer be necessary. Maybe we'll all be in Wall-E style bubble sleds and no one will be walking. Or car manufacturers will have finally agreed to get networked (against their will, as in the case of widespread commercial adoption of HTML/HTTP in the early 90s) in such a way that they can cooperatively handle most cases where person steps into the intersection and everyone can route around in a fraction of a second.