[mephistophelean]

Actually We don't really know what was in their minds when they led James away. I don't believe that either Venables or Thompson really intended to murder James that day. I believe that bravado played a hugh role and things got seriously out of hand.
We can't really take for fact what either of them stated during any interview with the police. Both may have said things that theyh didn't really mean but events overtook them.