Investigate, Tone
You say something about the circumference of this area. You've looked around this whole area, making a big circle around it, because you are trying to investigate something that happened here. You also say this thing in a really quiet tone of voice, because you don't want the person or thing you're investigating to know you're on to them.
Because the radical circumference is in play, you can think of the crime scene you're investigating as a statue of a giant globe, and you're doing a circumference around it. Then, in the reading, we'll think about what you'll say.
ちょう
しら
None
"I came here to investigate this place, and I did indeed find out who the criminal is... it's none other than Mrs. Chou (ちょう)!"
From what you know about evil Mrs. Chou, you probably could have guessed it was her. The "Circumference Investigation" is now over, though you do still have to catch the perp, Mrs. Chou.