If that's what they are claiming, I don't buy it. How convenient that Mom just happened to figure out that her son was the killer and call him in, all while the cops were figuring out how to charge him. Right.
Fact: many witnesses have come forward in the press now stating that AS was unsettling, odd, creeped them out, was "off." WS posters and people who know him have commented on his stare, that something in his eyes is unsettling.
Speculation: 1000s were interviewed during canvasses (presumably by uniformed officers, detectives, feds,etc. - all with varied levels of direct knowledge of the "guts" of the investigation). Futher: 500 DNA samples were taken ( by whom? CSI techs, beat cops pulled in for the purposes of the canvass due to a need for bodies?)
Supposition: canvassers, interviewers, DNA takers, etc may have been different persons, perhaps havng different interactions with AS during the course of the investigation, at different times, each experiencing him differently.
Say one of those individuals found him highly suspicious, another a little off and still a third not at all unusual, all based off their own interaction with him. Say there was no probable cause but someone found him worthy of a closer look. Would that info make it up the chain of command to trigger further digging into this suspect? How quickly? Would digging, if done, have given LE enough probable cause to further focus on AS, a minor?
Point (and there is one): hindsight is almost always 20/20, even for seasoned investigators.
Apologies for any typos, arthritic fingers and tablet typing do not mix well.