The alarm bar across the window won't let me open the window more than 1/4". I bought 2 havahart traps loaded with peanut butter - I'll try that. I may open the Bilco basement door and see if he will "follow the light" to outside. It's driving my cat nuts!
Once they get in, sometimes they're hard to coax to escape. You do need to trap him or leave something open for him to be able to easily escape.
But then you also need to figure out how he got in to begin with, and make sure that gets plugged off with something they can't chew through. 1/4" hardware cloth is often used. They can't chew through the steel mesh.