They kill journalists who expose their corruption, not that of other countries. They most certainly have someone tracking him, Snowden mentioned that he believe

They kill journalists who expose their corruption, not that of other countries. They most certainly have someone tracking him, Snowden mentioned that he believes as much in his interview. The US doesn't win much besides PR by getting their hands on Snowden at this point. The things he revealed have already had their consequences. Similarly, on the Russian side, it doesn't cost them anything to harbor Snowden, but it does make for a flashy middle finger to the United States.