It's like being jailed for having your car stolen and being used to hit a pedestrian.
Exactly this, except that nobody stole your car. You are providing free and no-questions-asked open access to your car for any member of the public who needs to use it. Many other people also used the car that day for legitimate business or for fun, but then one guy got in it and ran over 32 people in a furious rampage.
Clearly the driver is at fault here, but a case can be made (and apparently, was) that this would not have been possible had you not provided access to the car to the perp in question.