Although, I'm not ruling out the "hired perp" scenario, I agree with you, MissD, that the most likely scenario involves someone she knew.
Maybe an ex-lover (maybe even recent), maybe a friendly neighbor and/or lover and probably someone she was trying to end things with due to Allison's pending engagement (maybe even to cut financial ties).
The big question to me is how the perp entered the resident. Did she let the perp in? Did the perp have a key (maybe even returning a key)? Did someone else let the perp in?
I have lived in big cities most of my life and, even as a male, I don't ever open the door after dark to any stranger. I would like to think that neither would Allison.
The other important question to me is how does LE know when the perp left the residence. If LE knows the time from a camera, was the camera aimed at front or back of her house? If it was from a camera, does LE then also know when the perp entered the house? If not, why not?
For some reason I feel the perp left on foot which is possible why LE thinks they may be from the area.
JMO