For people out of the loop:

One of the first studies to investigate the rates of TBI in offender populations was conducted by Slaughter, Fann, and Ehde (2003) who reported the rate to be 87% in a county jail setting. Schofield et al. (2006) then reported the TBI prevalence in all offender populations to range from 25-87% and, later, Williams et al. (2010) documented the prevalence of TBI in those settings to be 65%. In a more recent study, Ferguson, Pickelsimer, Corrigan, Bogner, and Wald (2012) found that 65% of male inmates, and 72% of female inmates, reported at least one TBI resulting in a change in consciousness. Finally, some of the current authors studied the incidence of TBI in a mental health transition unit at a county jail and found the incidence of TBI among a sample of offenders with a co-morbid mental illness to be 96% (Gafford, McMillan, Gorgens, Dettmer, & Glover, 2015).

• https://psychology.du.edu/tbi

Why? He killed his wife in a fit of rage. There wasn’t anything special going on in his brain. A lot of pro athletes end up doing heinous crimes.

I mean, he had been abusive for years, it was sadly not a unique nor surprising case, except for his fame, but fame doesn't make you a good person.