Additionally, the fragments of broken glass were scattered in a homogeneous manner on the internal and external windowsill, without any noticeable displacement and without any piece of glass being found on the surface below the window. This circumstance...rules out the possibility that the stone was thrown from outside the house to allow access inside via the window after the glass was broken. The climber, in leaning his hands and then his feet or knees on the windowsill, would have caused some of the glass to fall, or at least would have had to move some of the pieces lest they form a trap and cause injury. However, no piece of glass was found under the window and no sign of injury was discovered on the glass found in Romanelli's room.
(The question to ask, when confronted with an argument like this, is:"rules out" with what confidence? If Massei and Cristiani think this is strong evidence against the hypothesis that the stone was thrown from outside the house, then that means they have a model that makes highly specific predictions about the behavior of glass fragments when a stone is thrown from inside, versus when it is thrown from outside. Predictions which can be tested(4). This is one reason why I advocate using numbers in arguments; if Massei and Cristiani had been required to think carefully enough to give a number, that would have forced them to examine their assumptions more critically, rather than stopping on plausible-sounding arguments consistent with their already-arrived-at bottom line.)
The impression one gets is that Massei and Cristiani thought, on some level, that all they needed to do was make the fake-burglary hypothesis sound coherent -- and that if they did so, that would count as a few points against Knox and Sollecito. They could then do the same thing with regard to the other pieces of evidence in the case, each time coming up with an explanation of the facts in terms of an assumption that Knox and Sollecito are guilty, and each time thereby scoring a few more points against them -- points which would presumably add up to a substantial number by the end of the report.
But, of course, the mathematics of probability theory don't work that way. It's not enough for a hypothesis, such as that the apparent burglary in Filomena Romanelli's room was staged, to merely be able to explain the data; it must do so better than its negation. And, in the absence of the assumption that Knox and Sollecito are guilty -- if we're presuming them to be innocent, as the law requires, or assigning a tiny prior probability to their guilt, as epistemic rationality requires -- this contest is rigged. The standards for "explaining well" that the fake-burglary hypothesis has to meet in order to be taken seriously are much higher than those that its negation has to meet, because of the dependence relation that exists between the fake-burglary question and the murder question. Any hypothesis that requires the assumption that Knox and Sollecito are guilty of murder inherits the full "explanatory inefficiency penalty" (i.e. prior improbability) of the latter proposition.
It is unlikely, though not impossible, that Guede would stage; but far more likely that the scene was not in fact staged...as you yourself state...
