The US Fair Punishment Project says "only a tiny handful" of prosecutors are responsible for a vastly disproportionate number of death sentences in the United States.
The Project has released a report, America's Top Five Deadliest Prosecutors: How overzealous personalities drive the death penalty.
It analyses the records of five prosecutors - only one of whom remains in office - saying they epitomise an over-aggressive and reckless style of prosecution.
"These prosecutors are evidence that the application of the death penalty is - and always has been - less about the circumstances of the offence or the characteristics of the person who committed the crime, and more a function of the personality and predilections of the local prosecutors entrusted with the power to seek the ultimate punishment," the report says.
Between them the five prosecutors obtained 440 death sentences, with former Harris County (Texas) prosecutor Johnny Holmes leading the list at 201 death sentences in 21 years in office.
Described by the report as "the worst of the worst", Robeson County (North Carolina) prosecutor Joe Freeman Britt is apparently listed in the Guinness Book of World Records as "the deadliest prosecutor in America". At one point, one out of every 25 death row inmates in the United States had been prosecuted by Britt, and a person in Robeson County was 100 times more likely to be sentenced to death than a randomly selected person in the United States.
"One of the most remarkable findings from our research is the fact that once these prosecutors and their protégés left their positions, death sentences dramatically declined in these jurisdictions - a pattern that has only become clear in the years since their departures," the report says.
Listing five "runners-up" who didn't make the five deadliest prosecutor list, and another "three to watch", the report says the profiles demonstrate that the death penalty has been, and continues to be, a personality-driven system with very few safeguards against misconduct and frequent abuse of power: "a fact that seriously undermines its legitimacy".
The Fair Punishment Project says it uses legal research and educational initiatives to ensure that the US justice system is fair and accountable.
It is a joint initiative of the Harvard Law School's Charles Hamilton Houston Institute for Race & Justice and its Criminal Justice Institute.