It will be next to impossible to drill downward under the portion of the roof that slopes to the attic floor without a right angle drill.
Finding inside of wall from attic.
Besides wall damage you may be able to hear dripping coming from inside the wall.
After all without a method to your madness you d just be hammering unsightly holes through your drywall in a vain attempt to cross paths with your wires.
To use it scan the device over the wall to find the area that has the highest moisture reading which will be where the leak is coming from.
I ran ethernet from our basement to a couple of bedrooms by passing the lines through where plumbing goes to the attic for the soil pipe vent.
If you notice any of these signs try using a moisture meter which can be bought at your local hardware store.
All holes around the edge of the attic need sealing with mesh wire screwed with screws to prevent mice from coming back.
When working from an attic space it will be significantly easier to access a wall space on the floor below by working either an interior wall or the exterior wall that is on the gable end of the structure.
Clean the attic first and remove any mice droppings and nests that you can find.
There are usually two openings far apart.
Squirrels need to be trapped so finding their access point is imperative.
How to get rid of mice in attic with blown insulation is a little different than a regular attic because of the insulation.