Which device was responsible?

Terrible 2013 bus accident in Boston raises questions about the responsibility of navigation devices (and / or their manufacturers / designers / sellers, etc). Especially interesting about this case is that both TomTom and Garmin are targeted, since it is unclear which one of two navigation devices was used. In Dutch law, if it is unclear which one of two agents committed a crime, neither of them is liable. Of course the comparison is not very good, as navigation devices are not autonomous agents. Yet, in the not-so-far future, buses will be self-driving and a ‘driver’ may have to chose between two ‘driving’ agents.