Yes, there are people on death row who have suffered from all kinds of shortcomings of the legal system. For instance, some people are on death row because the justice system didn't protect them from racism or some other kind of discrimination. It's sad that that's who we are as a people, but it's true.
If there are people on death row who are there due to fabricated evidence, they are in the minority. The majority of people do receive a fair trial or end up confessing to their misdeeds. I am not a supporter of the death penalty for many reasons, but this is obviously one of the problems with it. In many cases there's no guarantee that you're killing the person truly responsible.
While the majority of prisoners on death row are there because they are guilty or horrific crimes, sadly there are others who are there because of fabricated evidence. Fabricated evidence has become endemic in our justice system these days and the problem may become worse as the desire to have an absolute proof of guilt increases.
The vast majority of people on death row are not there because of fabricated evidence; rather they are there because the evidence shows that they are guilty. Most of the people actually did the crime. If there were not guilty by an overwhelming margin, they would not have received the death sentence in the first place.