How do we know that? The guy that was also prisoner that allegedly said that, recanted his statements as I recall. As for the police report: I wouldn't put too much money down on that being impartial, and not biased toward the police department.We know he was raising a ruckus in back for no reason. He very well might have done something stupid to try to continue to raise a ruckus despite being shackled.
Timeline!!
The guy was raising enough ruckus after being loaded into the van that the police stopped and shackled him. He wasn't hurt at that point, it wasn't about an injury. The other guy wasn't even in the van at that point, he couldn't testify about the situation.