I heard a few more details on this. He apparently sustained his injuries in the back of a police van . One of the things police do (if someone pisses them off or just for fun) is cuff a prisoner so that he can’t use his hands to protect himself and the drive around accelerating hard, braking hard whipping around corners etc to slam the prisoner around the inside of the police van. It administers a severe beating without the cops even touching their victim.
‘On Monday, police officers filed court documents saying that Mr. Gray had been arrested “without force or incident.”’
...and you know this how?
Sucks to be cuffed in the back of a police van then.