http://www.deathpenaltyinfo.org/node/523It isn't really known how many innocent people are killed each year in the American legal system. The true number might be quite high. Those at most risk of being executed when innocent are poor males. More so black males but white poor males are at significant risk also. These people suffer from inadequate legal representation. I think it was Marx who pointed out that rights are a great concept but they fail on the grounds that many are unable to afford legal represtation and thus can not secure those rights in court.
I honestly can't see how the death penalty can be regarded as consistent with liberalism. Of all the nations in the world, you'd think America, the great bastion of liberalism, would be most opposed to execution. Yet, despite their assertion of liberal ideology, and despite that they are personally at risk of being executed even though they are innocent, there seems to be wide spread support for the death penalty. I find this quite remarkable.