It was an electric chain saw, so it probably had like what…a 50 ft extension cord
Could've been cordless (Ryobi makes one; 18V power pack -- I suspect it runs for a *very* short period of time).
But, more importantly, electric chainsaws are 100% silent until you hit the button -- at which point they're at full speed almost instantaneously.
So you plug it in, you walk over to the victim, and you cut them a new one. Literally. And unless they look up and see you, they'll have no idea.
I still love what a friend of mine's mother did to her former husband one night after he slapped her. He woke up at 3 am to find his "docile" wife straddling his chest with a cast iron skillet in her hand. She informed him that if he ever
hit her again that he would not be waking up again. Ever.