Whether the death penalty affects the rate of murder or not

I visited the death penalty website which is talking about the death penalty in the US and its effect on the murder rate or not. The death penalty is not applied in all the United States. According to this website the murder rate in non-death penalty states has remained lower than the rate in states with the death penalty. This website shows us the rate of murder in 2000, which was up in states that apply death penalty, and it was 35% higher than states that did not apply the death penalty and in 2001, the murder rate in states with death penalty grew again to 37%.

In my opinion, this website is proof that the death penalty dose not affect the murder rate and they prove it by the figures, but I can't imagine or believe that, because in my country it affects the murder rate significantly.