Researchers in Southern California claim it is -- capital punishment works, they say. Why they draw that conclusion, and why critics strongly disagree.
Manny Babbitt was put to death in 1999 for murdering 78-year-old Leah Schendel. That year, there were 98 executions, more than in any previous year in two decades.
The following year, the national murder rate plummeted.
Darrell Rich was executed in 2000 after killing four women. That year, the number of executions dropped to 85 and the murder rate skyrocketed.
The two examples reflect the conclusion of a study authored by two professors from Pepperdine University in Malibu.
Professor Roy Adler is a professor of marketing, Michael Summers teaches quantitative methods. They claim their statistics prove the death penalty cuts down on the number of murders.
Their study concludes that when executions increase, murders decrease. When executions decrease, murders increase. In fact, according to their chart, each execution means about 74 fewer murders the next year.
Their study examined the correlation between the number of executions and murders in the U.S. during a 26-year-period from 1979 to 2004.
In the early 80's they say the return of the death penalty resulted in a drop in murders.
In the mid to late 1980's, the number of executions stabilized, the murder rate increased. In the 90's, more people were executed and the number of homicides plummeted.
Since 2001, the authors say a decline in executions has resulted in more murders.
"As far as the study itself goes, the research, design, the analysis, interpretation, they all appear to be valid," said Tony Ribera from the Institute of Criminal Justice.
Former San Francisco Police Chief Tony Ribera says the research is compelling. Ribera now heads the International Institute of Criminal Justice at the University of San Francisco.
"The death penalty is statically a deterrent to the crime of murder. Now, that doesn't mean you have to embrace it. It just means statically it is a deterrent," said Ribera.
Attorney Robert Bryan is the former chair of the National Coalition to Abolish the Death Penalty.
He says the statistics are seriously flawed.
"They've taken two sets of numbers and made this quantum leap that for each execution, we're saving a whole large number of lives. It's stupid," said attorney Robert Bryan.
Professor Robert Weisberg who teaches criminal law at Stanford Law School agrees. He says the study left out too many variables.
"Its true that states that executed people did see from the early 90s for about ten years a dramatic drop in murders but so did virtually every state," said Weisberg from Stanford Law School.
"In fact, the largest number of executions are carried out in the state of Texas. Texas also has a much higher murder rate than states that do not have the death penalty," said Bryan.
Ribera disagrees. He said using lots of different data would be like comparing apples to oranges.
"One might say there could be other variables that weren't considered. Police tactics, the economy, other things that might contribute to crime. It's hard to think that any of these factors could be consistent enough over 26 years to significantly impact the study that they did," said Ribera.
Gary Delagnes is president of the San Francisco Police Officers Association. He believes the study confirms what he's known anecdotally.
"When crooks talk to you in a very upright manner, they'd say 'oh I'd never commit murder in a state that has the death penalty. I mean they've actually said that to me," said Gary Delagnes from the San Francisco Police Officers Association.
The authors initially agreed to speak with ABC7 News but later refused, saying their study speaks for itself.
One thing seems clear: Among those who have taken opposing stands on capital punishment, the study probably won't change their minds.
Among the undecided, the study may pose some interesting questions.