That was always my assumption. Was going to say it, but you beat me to it! XD
I kind of also have to assume there is some vocal change as well, or he should recognize her voice.
I had first thought it was the cop too, but a number of things don't line up, like her being at work the first time we met Angel (IIRC), and her look. I even had a headcanon backstory worked out where she was tired of not being able to get things done within the system and such, even her supposed dislike for the vigilante was part of her cover, like you said, but then she seems more on the other side now, what with the whole thing we are blackmailing her about. On the other hand, many heroes have a vice... XDi think it is the cop, have they ever been seen at same time ? pretending to chase someone who is yourself will give you an alibi that it is not you, i mean you are her worst enemy
and there seem to be some clark kent effect where she appears after angel vanish and they never seen at same time.
also she is pumping at the gym a lot
Also, do we even know if his room has windows? I can't recall seeing them, nor reading a mention of them, but I might have missed it. If not, then that means that 'Angel' has not only been in your room, but the rest of your apartment as well. That reeks of familiarity. Either way, she not only knew where he lived, his name, but also what room was his and where to hide the letter. So, she is pretty likely to be more than just an acquaintance.
He could try analyzing everyone's handwriting... XD
