"Losing Faith" in the death penalty

Americans are "losing faith" in capital punishment, according to this Financial Times piece.  This passage, though, puzzled me:

Last week, a legislative commission in New Jersey recommended that the state abolish the death penalty, after it found "no compelling evidence" that capital punishment served a legitimate purpose, and increasing evidence that it "is inconsistent with evolving standards of decency".

What counts as "evidence" -- compelling or not -- that capital punishment serves a "legitimate purpose"?  I suppose if the "legitimate purpose" in question is general deterrence, then we could have the usual arguments about whether the death penalty deters.  But what about retribution?  What would count as evidence that the death penalty serves this purpose of punishment?  Or, does New Jersey think retribution is *not* a legitimate purpose?  Is the evidence to which the passage refers the kind of data the Supreme Court used in, say, it's recent execution-of-the-developmentally-disabled case, i.e., observations about trends in various states and nations?

Does anyone have a link to the New Jersey commission's report?