I think that much of this is going to depend on your exact assignment. If the paper is more of a personal piece, then I think your thesis statement can range in terms of being able to be an affirmation or negation of the death penalty. If it turns out that your task in the paper must be something a bit more complex, then your thesis statement can be aligned along that point. I think that the most important item to remember is that this thesis statement, like all, must be substantiated with support and analysis. You should select or carve out a thesis statement that is going to be reflective of what will be proven in the course of the paper. It is essential for you to not waver off task from this point. With a topic like capital punishment and the notion of the death penalty, it is essential to stay on track with the thesis statement. As you assemble the information that will form the essence of the writing sample, your thesis statement should be constructed with this element in mind. It is an intensely serious topic that you are writing upon and something that will require you to stay on message with it. Your message will become the thesis statement, so examine what you have and progress from there.