New Death Penalty Studies Reveal...what exactly?

I just read an article in the AP that studies have now proven that the death penalty deters crime. This cracks me up, because how many studies have gone the other way and shown that it doesn't deter crime? There have been numerous studies conducted that have gone both ways, some claiming that capital punishment does indeed deter crime and others stating the direct opposite. Some studies have even depicted that the death penalty increases crime, in what has been termed the "brutalization effect". So, what gives?

The methodology in this recent study does seem to be a bit questionable, in my opinion. It seems that they (the "researchers") took the number of violent deaths in a given year and divided that by the number of executions carried out and based on that data, it showed that with decreasing executions came increasing violent crimes and homicides. But, is the death penalty a red herring of sorts in the study? Can it really be said that all violent crime and homicides can be traced back to the use and prevalence of the death penalty? I'm honestly not thinking that to be the case.

If an execution was enforced more quickly, then there is a chance that it could deter crime, but that's not going to happen. With the documented cases of innocents being slaughter via the death penalty and the recent problems in Illinois, I can't see there being any way that executions will get carried out more quickly. Even if they would get carried out in a quicker manner, while it may deter some from murder, it may carry with it a bigger burden in terms of the before-mentioned brutalization effect.

It's also difficult to come to a precise conclusion on this matter, given the fact that so many countries have done away with the practice and crime has decreased in several of those countries since the abolition. So, again, can we say that the death penalty is a deterrent for crime in the U.S., but not in several other countries, including our neighbors to the north, Canada? Is the deterrence or level of it truly dependent upon such factors as location, weather patterns, economic status, etc.?

I don't know the answer to those questions, but don't believe we can conclude a practice such as the death penalty is a deterrent to crime based on a potential informal fallacy, in which all violent crime and homicides are related to the prevalence of executions in a given year and while there are so many studies and reports with conflicting results.