So, let's make two columns on how Gray was injured. In column A is the evidence that Gray hurt himself. In column B is the evidence that he was injured because of a "rough ride." In column A we write in Allen's statements. In column B, nothing. No evidence was offer at all of a "rough ride." So, yeah, self-infliction is probably more likely. I know, I know, there's your fantasy that Mosby's district attorneys chose not to charge Allen in exchange for him giving statements tanking their high-profile case against the cops. That'd probably be the worst
quid pro quo evah. But let's remember that all it takes to break a neck is just enough force at the right angle. Happens in football in wrestling. And this guy did it dancing to his favorite rave:
http://www.youredm.com/2015/12/14/guy-literally-breaks-neck-from-raging-too-hard/
So Gray hurting himself is far more plausible.