On its face, de Felice's statement means that the police suspected Amanda, Raffaele and Patrick before the interrogation on Nov. 5/6, 2007.
But it does not explain what objective evidence led the police to suspect them, or state that there was such evidence.
The police suspected them, and then conducted the interrogation to coerce the evidence that would (falsely) justify the arrests. It's the way the interrogation was done that constitutes the official misconduct. There was no evidence that a reasonable person would conclude justified the arrests before the coercive interrogation. As the Marasca CSC panel motivation report indicates, the motivation for the police - and prosecutor - included a desire to "solve" the case as quickly as possible. This motivation is what justified the "suspicions" of the police before the interrogation. They decided, for example, to completely neglect the downstairs crime scene. And without any objective evidence, they decided that the break-in was staged. Therefore, an inside job. Therefore, one of the flatmates was involved. Which one had the weakest alibi? Which one was the foreigner, barely able to speak Italian? Which one may have seemed very trusting and naive? Amanda. Therefore, she was suspected.
This is exactly the type of improper deductive process that I've long maintained occurred among the police and PM.
I think that as perhaps early as 2nd November, the police and PM had already convinced themselves (wrongly) that the break-in had been staged. And then, as you point out above, they inferred that the killer would have had to have been let into the cottage in order for there have been a need to stage a break in after the murder. They seem to have quickly ruled out the idea of Kercher letting the killer in herself, perhaps because they concluded that anyone doing a post-murder staging of a break-in (and the clean-up of the crime scene that they also wrongly thought had taken place) would have had to feel safe and comfortable hanging around in the cottage after the murder - they surmised that a "stranger killer" would have instinctively wanted to get as far away as quickly as possible, so that in itself pointed to someone who had a viable reason to be at the cottage.
And when they put all of that together, it pointed to a keyholder to the cottage being deeply involved in the murder - either the keyholder had let in the killer and conspired to clean things up and misdirect the police after the murder, or the keyholder was in fact directly involved in the murder. Romanelli and Mezetti had verifiable alibis for the whole evening.night of the murder, but Knox had an unverifiable alibi of having spent the evening/night with Sollecito in his apartment. The police/PM quickly concluded that it was therefore eminently possible that Knox was the keyholder they were looking for, that she was lying about her whereabouts on the night of the murder, and that Sollecito was either lying to protect her or Sollecito was also involved. The fact that Knox had acted in an unorthodox and (arguably) somewhat inappropriate fashion in the hours and days following the murder only helped harden the views of the police/PM towards her.
And then the police started trailing Knox, tapping her cellphone and obtaining her cellphone records from around the time of the murder. Knox had not mentioned any phone/text exchanges on the evening/night of the murder in her interviews with police, but now the police could see a text exchange with a number at a critical point on the evening of the murder. It's hard to know whether the police were able to identify the correspondent with whom Knox was exchanging these messages simply from the cellphone number, but IMO it's a racing certainty that the police became convinced that this text exchange was extremely important, and that Knox and the correspondent were now key suspects. This would have all happened by either late on 4th November or early on 5th November.
Another thing then happened on the afternoon of the 5th November which solidified the belief of the police/PM in their theory of the crime. The police surveillance team witnessed Knox having a serious conversation with Lumumba outside the University for Foreigners. Whether the police had by this point identified Lumumba as the correspondent in the text exchanges on the evening of the murder, the police/PM clearly decided that this conversation on the steps of the university was a surreptitious meeting between Knox and Lumumba to discuss what Knox had and had not told the police, and whether or not they were in the clear, etc.
So I am of the very, very firm belief that by the early evening of 5th November 2007, the police and PM had concluded that Knox was deeply involved in the murder - that she had either 1) assisted the killer (whom I think they by now "knew" to be Lumumba) by letting him into the cottage, cleaning up and staging the break-in after the murder, and lying to police to protect him after the murder, or 2) participated in some way in the murder itself, alongside Lumumba, and then conducted the clean-up and staged break-in. And I think the police/PM believed that the way to entrap Knox was via Sollecito: they believed that it was most likely that Sollecito wasn't anywhere near as deeply involved as Knox, and therefore had far, far less to lose by "coming clean" and telling the truth. I am confident that at this point the police/PM believed the most likely scenario was that Knox had asked Sollecito to lie to the police by saying that she was with him in his apartment all evening/night, and that Sollecito had agreed to lie because he was either besotted with her or afraid of her.
And then...... the police/PM learned that Knox's mother was en route to Perugia, and was due to arrive on 6th November. The police and PM were suddenly placed under huge time pressure, since at that point they had no mechanism to compel Knox to remain in Italy, and they were pretty certain that Knox's mother would be taking her back to Seattle as soon as possible, maybe even leaving on 6th November.
So now time was of the essence. The police needed to garner sufficient evidence to arrest and detain Knox before she had a chance to leave Italy. Therefore a plan had to be constructed and enacted immediately. The Perugia police HQ was staffed up with detectives of the night of 5th/6th November. The plan (IMO) was to call Sollecito in on his own, and get him to admit that he'd been lying to protect Knox. The police would tell Sollecito that they had solid evidence that Knox was involved in the murder, and that Sollecito was only placing himself in grave legal jeopardy by lying to protect her. Since the police genuinely thought that Sollecito HAD been lying to protect Knox, and that Knox HAD left Sollecito's presence that night to play her part in the murder, they reasoned that it wouldn't take much for Sollecito to "tell the truth" and abandon Knox.
And once that happened, the police would have all they needed to go out and arrest Knox and bring her in. I strongly suspect that the original plan was that a surveillance team would have been keeping close tabs on Knox's location, such that an arrest squad would be able to go directly to her location (probably having tipped off the local media in advance, so that there were film crews on hand to capture the triumphant moment of arrest) and arrest her with maximum fanfare. The police would then confront Knox with Sollecito's withdrawal of his support for her alibi, give her the good old "Sophie's Choice" along the lines of "tell us the truth and things will be a lot easier for you; keep lying to us and you'll be looking at 30 years in prison", and Knox in turn would break. The arrest squad would then go out and arrest Lumumba in turn.
Of course things didn't quite turn out as per the plan. Knox came in with Sollecito, thus denying the police the chance to arrest her in the glare of the the TV lights from Sollecito's apartment (or wherever she was at the time). And Sollecito didn't "buckle" in the way the police had assumed he would - on account of the fact that he actually WASN'T lying to protect Knox. Instead, the police hammered away at him until he became so confused that he mixed up dates and amalgamated events from the night of the murder with those of the night before the murder (Halloween). But the police decided that was good enough for them to move onto the next phase.
Then Knox was brought in for interrogation. Very quickly, the final element in the "perfect storm" hove into view: the examination of the content of Knox's final text message to Lumumba on the evening of the murder. It was cast-iron confirmation to the police that Knox truly had arranged to meet up with Lumumba that night, and that she'd lied to them by having claimed to be with Sollecito in his apartment all evening/night. All the police now needed to do was to use all means necessary (and all unrecorded, of course....) to get Knox to "buckle" and "tell them what they already knew to be correct".
Poor old Artur de Felice didn't realise just what a gigantic mistake he made when he triumphantly crowed to journalists in that hubris-packed press conference the following morning that the police had, in effect, already solved the case before Knox even entered the interrogation room late in the evening of 5th November, that the police already knew Knox had been lying to them up to that point, and that the police got Knox to "buckle" and tell them what they
already knew to be correct. Never was the phrase "pride comes before a fall" so apt........