Ranpo has never had difficulty solving cases...He's never actually struggled when solving crimes or finding culprits, so when your Mafia group came to the city he thought it would be a breeze to track you down and arrest you...

He was able to find your location easily but when he found you, you were a blank slate...You were smug for sure, but he couldn't figure you out at all...You were just blank...So of course he didn't let them arrest you...He's gotta deduce everything about you first...