It is obvious that if they can consider releasing him as a political pawn that he is being held for political purposes in the first place. If his release was a danger to US security it would be completely irrelevant as an incentive. It becomes clear that he is only being held at this point out of spite.
Russian defense ministry: Plane sent to intercept U.S. plane near border on Friday (Reuters)
from the article: Pollard's actions 'exceeded only by Snowden,' ex-U.S. official says