The NSA is one of a number of agencies responsible for such work. For example, the Boston terrorist suspect was on the Russian watch list and they informed the U.S. about such an individual. Apparently there are other cases of collaborative work in prevention of terrorism. Snowden holds the information which has been compiled for years about potential suspects. Russia, therefore has an obligation to collaborate with the United States as the data belongs to the United States government and not Mr. Snowden.
Death toll from car bombs in Iraq rises to 56 (AP)
from the article: Putin: If Snowden wants to stay in Russia, he must stop harming U.S.