If Miss Sakamoto could activate the action replay for a second....
This diseased maniac is very fast on his toes.
He is also very stealthy.
Sneaking up on him would hinge on knowing exactly where he was going to strike.
Now in this situation you have a near infinite number of nurses and presumably more than one perp (unless he has some kind of teleport device we don't know about).
Maximum carnage could be achieved if you fitted some kind of bottomless pit in the path of the victim but hooked up to a colour detection device.
The nurses are wearing some white but the red cardigan may be a life saver as it could bleed enough colour onto her uniform not to trigger the detector.
Even near bottomless pits can be very effective as seen in this scientifically accurate crime scene reconstruction:
