I don't know of any way to make an action appear to only one side in *singleplayer*. In multiplayer, addAction only gives an action to the player whose computer executed the command. So if you're making an MP mission, then modify savedbygrace's conditions for the first trigger to:
officer distance thief <= 1 && officer == player
and probably also give the second trigger
officer distance thief > 1 && officer == player
But if this is a singleplayer mission, perhaps we can find a workaround.
Am I correct in assuming that the thief would be the player? If not, then no need to keep him from seeing the action, because AIs will never execute added actions of their own accord.
If he is a player, then savedbygrace's solution will probably work, unless the player would somehow want to get himself arrested.
But actually, all you would need to do to get the player arrested when the cop comes up to him is place a trigger as follows:
Condition:
officer distance thief <= 1
On Activation:
player switchmove "FXStandSur"
Even players cannot move when they've been forced to perform that action.