Shaker et al might still have succeeded
At the time Mullen offered the $2M dead-or-alive reward the identity of the ringleader wasn't yet known, apart from suspecting Clark. They could've bumped off any random homeless guy, a petty criminal or even Clark, drop the stiff and kid somewhere and then tip off Mullen about the location. After the hubbub was over they merely had to contact Mullen again with some story about being mobsters or such (perhaps disgusted with lowlife kidnappers), hence not wanting to step in the limelight and having to answer awkward questions from the man. Mullen would have his kid back at this point and be more than delighted to fork over the cash.
Better than the alternative.
John Kenneth Galbraith, when asked what it was like to have reached the age of ninety.