purely use when
Perhaps the accused didn't want to answer without legal representation - you said "scene" after all. Perhaps the accused didn't want to say anything before getting legal representation. Perhaps the accused just expected they could exercise their rights without their being any punitive results.
using
Advising them of their rights, and the caution is not just for the police officers benefit.
When else would somebody it be relevant for somebody to be silent?
And what if the owner genuinely doesn't know. As a private individual, they are not expected to be responsible and keep records at all time, like a business is. So what then - what's the likelihood?
What if the car had been cloned ringed - who or where do you thing the onus of proof would be on?
No - it's tantamount to be presumed guilty, until you can prove otherwise.
alternatively,
What's likely to happen if you say: "I wasn't the driver, and I don't know who was at the time"?
Quite.
What if they genuinely don't know?
It's not beholden on them to keep records. Perhaps numerous family members can use the vehicle. Hey, even some high-ranking police officers have claimed that.
car,
I would expect the burden of proof to be more than simply buttuming it's the registered keeper, who's keeping sh'tum.