How to kill with a defibrillator (Battlefield 4)

Please explain what I am doing wrong. I would like to complete the task of obtaining the L85A2 barrel. Enemies are not killed by a defibrillator, although I resurrect my own without problems. I sneaked up to the enemy from behind and turned on the defibrillator three times - zero emotion, the enemy sooner or later noticed me and killed me.