I am new to this thread, but have been highly intrigued by Evelyn for awhile. I read through almost all of this thread over the past few days - I don't believe anyone mentioned the idea that maybe Evelyn thought the family was returning home, thinking they forgot something. They wouldn't have been gone long and maybe she opened the door without checking first. She could have thought they forgot their key. The radio could also could have been on louder than the sound of a car pulling up. Side note - I found it intriguing that they even locked the doors. I am from around the area and have heard the old idea that no one really locked their doors during this time period, though I guess I don't know much about the self-locks that were on the house. Still seems a bit odd to me they would even have these on their doors at this time, but maybe it just came with the house as a "state of the art" type thing or maybe they had them installed after the peeping tom? It's a stretch, but the Professor also could have been worried about angry students breaking into his house?
What was the location of the baby's window? Maybe Evelyn was putting her to sleep when she saw someone outside. She could have saw them actually trying to open the windows and ran to call the police, not thinking they would actually get in. Or, she heard a noise while with the baby and went to investigate, thus the shoe in the basement. Perhaps it was a bit of both - She saw and heard the person breaking in. The time frame was relatively short from when she put the baby down and from when she was supposed to cover her.
The father going to the neighbor's house to use the phone also confuses me. How close was this neighbor? I am not sure if I am just misremembering, but did someone say it was across the street? That also means at least 3 people in this tiny neighborhood were home, since there was the couple that heard the scream and this man (IIRC, I don't think this man was the husband of the couple). So I am leaning towards them personally targeting Evelyn/the house.
Just thought I would contribute some of my thoughts. I found the man and woman theory the most intriguing, though the tapes also make me wonder. I apologize for the rambling, I am trying to sort through my thoughts.