I do not think it would be as difficult as it may seem. The mansion wall is composed of bricks and stone, yes? The surface is uneven enough that it would simply be a matter of finding a foothold and being strong enough to pull yourself up to the window ledge. In which case, anyone with sufficient strength and reach should be able to do it. Perhaps we can test it out with someone strong enough who is not a suspect?

Yes...I am not sure if there is a poison or chemical that would only cause one eye to dilute but not the other when ingested.