RSBM
Possibly after the killer finished, and the rage subsided, he didn't want to look at his handiwork, or perhaps he was reminded of the presence of the boy, and covered Mama's face to settle him.
But there were several "unwanted admirers" in her life. He could also very well have been a customer where she worked-- someone she didn't really pay any attention to (and it angered him).
If the killer was also the obscene caller, he could've deduced there wasn't a man in the home, through the obscene calls. He spoke with both Angela and Beverly, depending on who answered.
What strikes me is that the ad was neatly clipped, not torn, from the paper. And it was completely removed from the newspaper, as opposed to the newspaper being left there, with the ad circled.
Also the "circle" appears to be made by a rubber stamp. So who used a rubber stamp (with an oval) and red ink in their profession?
I wonder if he could've been a mailman or utility worker (meter reader, etc), or posing as one. That would allow him to carry a bag containing the "tools" to commit the crime into the house without attracting attention.
I partially disagree with Godwin's assessment, but the case is very solvable. All just my opinion.
