The other area highlighted in DPIC's annual review are exonerations, with seven former death row inmates being freed in 2014 – the highest number since 2009.
The first prisoner was freed from death row by DNA evidence in 1993, other high-profile exonerations followed.
North Carolina alone saw three exonerations in six months in 2008.
Neither supporters nor opponents of the death penalty are happy with this odd result.What Americans really want is an error-free death penalty, but this can never be guaranteed, as the recent spate of death-row exonerations has shown.
Widely reported exonerations have alerted the public to the uncomfortable fact that juries are sometimes biased, that the police sometimes lie and that snitches often do.But what if executions save lives by deterring potential murderers?
Some high-profile exonerations have also illustrated the frailties of the justice system, and years of death-row appeals are terribly costly for states.
Go to the website of the New York-based Innocence Project to see the latest tally of exonerations that have taken place in America, after DNA evidence showed those convictions to be unsafe.
The New York-based Innocence Project, which provides free legal representation to people who it hopes can be exculpated on the basis of DNA evidence, counts no fewer than 268 such exonerations since 1989.
Mapping the death penalty in AmericaFROM 2000 to 2011 there were, on average, five death-row exonerations a year in the United States, according to the Death Penalty Information Centre.
Mr Watkins wanted prevention and rehabilitation, but exonerations came first.
Her firm "is looking forward to adding Mr Avery to its long list of wrongful conviction exonerations", it said in a statement.
