What makes you think that there has to be single, complete theory that explains the crime in order to convict?
If the evidence is too incomplete to give a definitive answer, there should be even more then one scenario fitting that evidence - the less of the facts are known the more is open to assumptions and interpretation.
Neither Massei, nor his supporters, despite taking freedoms with assumptions and interpretations are able to provide even a hypothetical but still believable and comprehensive scenario of events.
This is troubling, because on the other side it is not hard to draw a scenario in which Amanda and Raffaele are victims of a mistake. Erroneous interpretation of phone records, led ILE to view defendants' behavior with a certain bias. The ensuing mistake of ascribing Raffaele's shoes and his knife to the crime scene (both of the items he brought to the Questura on Nov 5) and the following unlawful interrogation sealed their fate and staged the tragedy.
The fact that there is no conclusive or sufficient evidence of their involvement, and what is there is highly controversial works in favor of that latter scenario.
The single perpetrator scenario don't suffer from such "bottlenecks" of probability like the Massei theory. There is no need to stretch the ToD, and moving that ToD by a few minutes doesn't topple the whole case. There is no need to contrive any implausible stories in which strangers are enrolled to help in a murder or 30 cm kitchen knives are carried for protection etc.
Summing up - if Massei or his supporters were able to conceive some explanation encompassing the known facts, we would have something to consider and compare with the lone wolf scenario.
So far nothing like it emerged and it won't, because there will be no new facts indicating AK and RS guilt, only more facts revealing the truth.