You simply can't trust the North Koreans. They lied to President Clinton when they talked him into sponsoring their nuclear program. It's a simple truth, you can not trust communists under any circumstances. Their word, written or spoken, is worthless and they only do what they perceive to be in their best interest or what they are forced to do.
Bilateral talks mean Kim Jong Il extorts America. Multilateral talks mean Kim Jong Il has to hold a gun to the heads of five countries. Kerry is Carter II.