The report, which drew from court and prosecution records over an 11-year period, concluded that a white victim increases the odds of a death sentence by 8 percent. When the victim is black, the chances are 6 percent lower.
"The race of a victim and the type of representation afforded to a defendant play more important roles in shaping death penalty outcomes in Pennsylvania than do the race or ethnicity of the defendant," according to the 197-page report obtained by The Associated Press.
Penn State researchers produced the $250,000 study for the Interbranch Commission for Gender, Racial and Ethnic Fairness, and its findings are expected to be incorporated into a separate, ongoing review of the state's death penalty that Democratic Gov. Tom Wolf has said could affect the death penalty moratorium he imposed shortly after taking office in 2015.
The report also found the prosecution of death penalty cases varies widely among counties, calling that variation the most prominent differences researchers identified.
"A given defendant's chance of having the death penalty sought, retracted or imposed depends a great deal on where that defendant is prosecuted and tried," they concluded. "In many counties of Pennsylvania, the death penalty is simply not utilized at all. In others, it is sought frequently."
Lisette McCormick, the commission's executive director, said the variations suggest an arbitrary element at play in the justice system.
"A system in which a death sentence can be imposed must be uniform across the state," McCormick said. "The chances of having the death penalty imposed should not vary depending on where you live in the state."
Pennsylvania has a death penalty on the books, but its death row has shrunk to 157 men and only three people have been executed since capital punishment was reinstated in the 1970s. All three had voluntarily relinquished their appeals.
The study noted that blacks make up about 12 percent of the Pennsylvania population, yet they make up more than half of those sentenced to death.
Wolf has said he was concerned about what he called a "flawed system that has been proven to be an endless cycle of court proceedings as well as ineffective, unjust, and expensive."
Researchers with Penn State's Justice Center for Research said there was no "overall pattern of disparity" by prosecutors in seeking the death penalty against black or Hispanic defendants, but did detect a "Hispanic victim effect" in which prosecutors were 21 percent more likely to seek death when the victim was Hispanic.
Black and Hispanic defendants who killed white victims were not more likely than a typical defendant to get a death sentence.
In nearly a quarter of all cases, defense lawyers did not present a single "mitigating factor" to push back against the aggravating factors that must be proven in order to justify a death sentence.
"There are plenty of public defenders that don't have the time or the resources to be able to conduct a proper investigation of the strength of the evidence," McCormick said.
With the exception of Philadelphia, which has a unique system for providing lawyers to those who can't afford them, defendants represented by public defenders were more likely to get a death sentence than those with privately retained lawyers.
Unlike studies in some other states, the researchers said there was "no clear indication" that defendants with private attorneys — as opposed to court-appointed counsel — were more likely to get a plea deal with prosecutors that avoided a death sentence.
The 18 counties in the study included many of the state's more populous areas, and generated nearly nine out of every 10 first-degree murder convictions over the study period.