The way I remember it was there were 'multiple' unnamed sources that said his sister was suspicious of his behavior after the murders when he was back at home "over the holidays", and a subset of those sources said it was both of his sisters, who later looked in his car.
This is IMO, because I don't know which MSM articles this information was in, or if it was an approved source here on WS. Or if it was accurate, but I think it generally was. If my brother came home from 2/3rds of the way across the country a month after 4 coeds were brutally murdered 11 miles from where he was living, and his car matched the description of the car LE was searching for, I would be seeing big red flags, and be suspicious as h e double toothpicks. Even if I had never had any concerns about his behavior in the past.
Speaking of his behavior, I think part of the reason she/they may have been suspicious of him was because the whole family probably observed him sorting trash streams, and may have heard or seen him going out in the middle of the night to put trash into the neighbor's bin.
Such weird behavior when home for the holidays, "even for him", IMO. I wouldn't put it past him to act extra suspicious around his family to put them on alert, if he wanted to get caught.
Re the April amazon knife purchase, I also remember seeing that in the news. IIRC, it was maybe a leaked detail that was not just speculated on from search warrant results, and was from an unnamed source, or it was wholesale speculation with an unnamed source.
There's also a sliver of possibility in my mind that the April 2022 amazon knife purchase evidence (the receipt) slipped through the cracks between the initial drafting of LE's PCA and BK's arrest warrant, and the judge's approval of the gag order.
If LE were already doing searches / data mining of big online retailers selling a certain kind of knife that could be the murder weapon before the gag order was official, some info on results of those initial searches for the murder weapon purchaser could have surfaced, IMO.
"What the gag order says
The arrest warrant and criminal affidavit for Kohberger were issued on December 29, 2022, and within a week the prosecution and defense jointly agreed to a gag order.
The January 3 order states that "investigators, law enforcement personnel, attorneys, and agents of the prosecuting attorney or defense attorney, are prohibited from making extrajudicial statements, written or oral, concerning this case, other than quotation from or reference to, without comment, the public records of the case," Magistrate Judge Megan Marshall wrote.
The order specifically forbade commentary on evidence of occurrences or transactions, the character or criminal record of a party, opinions about the merits of the case and "the existence or contents of any confession, admission, or statement given by the defendant.""
Why judges use gag orders in high-profile cases like Idaho student murders
