Fantastic! I struggled so much with this one as well trying the same challenge, messing about in that small technical room (of which you can’t manually close the door) he passes by, but always getting caught a milisecond before hiding his body.
Tried playing around with the accident opportunity by the ground floor bathroom. After dispatching of NPCs with line of sight, and the target’s roaming guide and guard, I stood over by where the staff entrance barrier is and shot the valve and light-art-cube on the ground right in front of the valve. The electrocution reached across the hallway and killed me.
That must be the biggest puddle-electrocution zone I’ve seen in this game.