The WP published the story about the lead poisoning court case because conservative news sources were apparently wrongly claiming it was a court case for spinal damages received in a car crash. The WP says Gray had NOT suffered any previous spinal injuries; well, he was fit enough to run away from the police.
The WP said lead poisoning causes behavioural problems, aggression, bad decision-making. They were trying to counter the demonisation of every black male killed by the police: he was a criminal, he ran away, his own fault ....
It seems possible Gray suffered some spinal injuries during arrest, when witnesses reported his legs & back were bent "like a prezel" Possibly also someone put a knee on his larynx, which is when it was ruptured.
Anyway, he was handcuffed, feet shackled and put in a van without seatbelt or safety bar. So, he would have been thrown around, possibly intentionally. Any spinal injury would have been worsened. The autopsy apparently showed his broken spine required tremendous force, far more than he could have inflicted on himself (debunking another conservative theory)
Some US police forces have paid out millions in damages for suspects given a deliberately rough ride and seriously disabled.
The van driver is the one who was charged with the most serious offence, 2nd degree murder, which adds weight to that theory.