There's zero evidence that RB's investigation wasn't a proper one, no. Certainly not publicly at the very least.

But then again, RB's owners have done some... legally questionable things.

The Thai owner's son hit a police motorbike and dragged him over 100 metres along the road, killing him in a particularly gruesome way, while he was drink driving. He then fled the scene of the crime.

The family initially implied a driver hired by the family was driving, before it being discovered it was the owner's son/heir to RB.

The initial police investigation had to be disbanded because it was found they were attempting to cover up the crime.

The RB owner's son then fled the country, and the family lawyers kept telling the courts he was too poorly or busy with work to attend court.

Finally, after 5 years and lots of legal back and forth, the police put out an arrest warrant.

He still hasn't received any punishment for his crimes.

Obviously these are two very unrelated matters, and Horner should still be presumed innocent unless there's evidence to the contrary. My point is only that I don't find it implausible that the RB owners would brush bad shit under the rug or do something dishonest/legally questionable. They have form.