He was to grow up the US with hypnotic commands planted deep in his subconscious that would cause him to report intelligence back to Castro.
It’s a win-win situation for Castro. If the US decides to obey it’s own immigration laws and send him back, Castro wins a political battle. If he stays, then a potentially useful spy is accepted in the US.
Send the little commie back to uncle Fidel! In chains!
OK, seriously, this actually isn’t a bad idea. Substitute the hypnosis for something a little more plausible, like a simple brainwashing, and it might work.