Make no mistake, the worse thing you can do is to send this guy/gal into a frenzy by locking him/her in.
I would do exactly as Jason stated and I would do some more things to make him/her realize that this place is not safe.
You never really know if you got all the guy/gals in the attic anyway. You don't know how many entered and how many exited.
So, here is what I have done before on the very same situations:
Identify the areas where they come and go. The claw and scratch marks clearly gives that away. Get a rotating head full size owl and perch him near the entrance. handle this guy with latex gloves as to not leave your scent on it.
Then go to a sporting goods dealer that specializes in Archery supplies, and get some fresh, yes fresh, red fox urine. Spray this around the opening. It will disolve with a rain, so re apply after the rain.
This stuff comes in a small bottle with a spitzer spray atomizer. Do not spray into the wind or you know what.
Let this program work for about a week or so, then when the noise stops and the scent and owl do their thing, board the thing up and use metal flashings at all corners.
Try to trim all overhanging tree branches away from your home so he/she cannot hop or jump from tree to your house.
A red fox is a very sly, sharp, hunter and all others will scamper like a hawk around birds.