And as anyone familiar with the case know, Rudy Guede is the one person involved who certainly knows exactly what happened when the murder occurred.
If he says 9:20 - 9:30. He's right. You can ignore all the other lies he has told (or was fed, and sort of told to say, is another way to put it)
As far as the TOD goes. Rudy's right. That's it. There is no reason for, or gain in him lying. It's one thing he would sit there and reply to honestly, without being wary of any need for obfuscation of the event.
Of course the more idiotic of the pro-guilt commentators will leap on this issue and say something like this: "Oh, I see, Rudy's a complete liar when it comes to him accusing Knox and Sollecito of participation in the murder, but when it suits you he's suddenly telling the truth about the time of the scream!"
But of course this "argument" is not what it seems, and it's easy to rebut. As you say, it comes down to what is/was in Guede's best interest to claim. Clearly it's in Guede's best interest to claim that he had no involvement in the murder, although he knows from the bloody palm print that he can't escape the fact that he was in Meredith's room either during or shortly after the murder. And this is exactly why he invented the convoluted story about being in the cottage but on the toilet at the time of the attack, then rushing back into Meredith's room as the "real killers" rushed out (scuffling with him and insulting him on the way out). He then seeks to explain his bloody hand print and shoe prints in Meredith's room by pretending that those were deposited while he was trying to help the dying Meredith. Of course all of this is directly contradicted by his nonchalant appearance at the dancefloor in Perugia within hours of the murder, so we can be pretty certain that his explanation in regard to his movements within the cottage and non-participation in the attack are a bogus concoction.
But when it comes to the scream and the time of the scream, there's a different dynamic. Guede makes it clear in the Skype call that the scream was loud, and even explicitly states that it was loud enough to be heard from the street. To me (and to most rational people), this is very telling. It seems highly likely that Guede was afraid that one or more people outside the cottage might have heard the scream. He therefore realised - as he did when addressing the problem of his bloody hand print and shoe prints - that he needed to weave the scream into his bogus narrative. Importantly, he also realised that he needed to place himself away from Meredith's room at the time of the scream. After all, if he had claimed that he was still getting intimate with Meredith (uggghhh) until 9.45pm, and a witness had subsequently come forward to testify that there was a loud scream at around 9.20, Guede would immediately be in big trouble.
So Guede knew that he had to a) include the scream in his narrative, and b) make sure that the timings "worked" so that he placed himself in the bathroom at the time of the scream. Thus he is very probably correct when he places the scream at "9.20-9.30": the correct timing is crucial to the preservation of his bogus narrative.
Incidentally, Guede still has an additional insurmountable problem to overcome regarding his narrative, and it's this: he knows that there was a loud scream at around 9.20, so therefore he has to place himself in the bathroom at that point in time (in case someone heard the scream). But he also knows that he has to account for the evidence of his interference with Meredith's genitals. So he invents the crap about engaging in consensual sexual contact with Meredith.
But here's his problem: it's incontrovertible that Meredith didn't arrive back at the cottage until around 9pm (although it's interesting to note that Guede didn't at that point realise how precisely this time could be established, and thus he claims that he met Meredith before 9pm). But Guede's narrative requires him to spend quite some time sitting on the toilet - in order to give time for the "real killers" to enter the cottage, confront Meredith, and attack her. So that's why he works back from the 9.20 scream and has to place the start of his visit to the bathroom at around 9.10. This gives his story the requisite 10 minutes for the "real killers" to enter, confront and stab, while he (Guede) sits in blissful ignorance on the toilet listening to his iPod (which also gives hi an excuse for not hearing any escalating argument or other preamble to the stabbing).
So, where are we up to? Well, Guede knows that he has to work back from the 9.20 timing of the scream. He also knows that he has to place himself in the bathroom for a good 10 minutes prior to the scream, in order to support his story of being oblivious to the "real killers" entering the cottage, confronting Meredith and killing her. He therefore knows he has to pretend that he left Meredith's room to go to the bathroom at around 9.10. But he also has to try to explain the sexual contact, so he invents the story of consensual heavy petting. But since Meredith only arrived home at around 9pm, and since Guede has to pretend that he went to the bathroom by 9.10pm,
this only leaves a 10-minute period for Guede and Meredith to a) meet, b) have some sort of discussion, and c) engage in all the escalating heavy petting that Guede needs to claim took place. This is yet another clear indicator that Guede's story is scuppered by the timings that he knows he has to weave into his narrative.
