Since you mention him taking things, this version of the power obviously lets the user manipulate the environment while time is stopped.
Almost all the applications of the power are sneaky by definition: no one else can know anything is being done until after the fact. Depending on time restrictions and other limitations, properly used it should be almost impossible to identify the perpetrator of the crimes short of finding him in possession of stolen goods/abducted people. Sneaky applications include planting evidence on others both to embarrass and to frame once the crimes are detected. Assassination is easy; stop time place the target in a potentially lethal situation (like on the wrong side of a balcony railing or holding a shotgun against his chest with the trigger pulled), leave and allow time to restart. If people are stupid enough to carry weapons near the villain, stop time take a gun from one shoot at the rest, put the gun back where you got it, move back to where you were and let time restart and see how good your aim was. The survivor can have a merry time explaining to the police why his gun -- the one found in his holster at the scene -- is the one that shot the rest of his team.
As for stopping the villain, I recommend a sniper from 500+ yards or poison subtly administered. You have to inflict sufficient damage to negate his ability before he becomes aware he is being targeted.
Like most powers, it is ethically neutral. What matters is what one does with it. Few would quibble if one decides to take extra-long hot baths and time was stopped to facilitate reading more pages of a book before the kids come home. Most would object if murder, abduction, and mayhem were the result of the power.