There is plenty of historical precedent that suggests that someone "hanging themselves" in jail is quite likely to have actually been hanged, as it's a relatively easy way to dispose of someone hated, with a very low chance of it being investigated or found out. After all, "They won't be missed".
Sadly, we as a society don't do enough to combat this sort of thing. We aren't bothered by the possibility that someone was unjustly executed via corrupt jailers or vigilante prisoners, because we consider it to have been "deserved", to be some sort of Providential punishment for their crimes.
Yet we are ostensibly a nation and a people of laws, and Justice demands that we are all equal under the law, even those we condemn and revile for terrible acts. Petty vengeance corrupts us, twists us, deprives us of any moral standing and turns us into hypocrites of the worst kind. Let the law do its work - let those who commit crimes be subject to the powers of law - but do not turn a blind eye to further criminality, or even merely to the possibility of such, no matter how "deserved" we feel it may be.