In Mockingjay, does Katniss kill Snow?
Snow dies in the book Mockingjay. Katniss chooses not to kill Snow though. Remember, Katniss wanted the right to execute Snow herself when it was all over. Her and Coin came to an understanding that they both wanted to kill Snow and that after the reolution, they would decide who got the right to take his life. After the revolution, Snow is kept hostage in the palace in his room with his roses, and Coin offers the execution to Katniss who gladly accepts.
However, Katniss is still incredibly damaged by her sister's death. Before the execution date, she goes roaming the house to find a rose to pin on Snow's jacket before Katniss kills him. Snow is there, and he tells Katniss that those ships that dropped bombs on the innocent children were not his. Strategically, it made sense for the revolutionaries to drop this bomb and make it look like it was the Capitol and turn every member of the city against Snow.
On the final day of the execution, Katniss draws back her bow and shoots Coin. The crowd goes crazy, and in the pandemonium, Snow is trampled and killed. You could argue that it is Katniss's fault that caused the pandemonium, however I would argue she makes a conscious decision to kill President Coin over Snow. It is a lesson in power and how even in a revolution, the revolutionaries may not be necessarily improving the quality of life after the revolution.