Insofar as whether heroin causes hallucinations, Curatolo is absolutely right. Heroin no more causes hallucinations than paracetamol or any other non-hallucinogenic drug for that matter.
A drug user who only uses heroin is a rare beast, criminologically speaking, and heroin addicts are typically polydrug users, which is a fancy way of saying they will shove anything they can get into their nose, mouth or arm. So it's more likely that Curatolo was on LSD or something on any given night than a randomly selected member of the population, if that's all we know about him, but not greatly so.
Some forms of mental illness can cause hallucinations as well but I am not aware that Curatolo has been diagnosed with any such condition.
His track record of popping up with just the witness statements the Perugia police needed is also hard to reconcile with the theory that he was randomly hallucinating, whether because of drugs or some underlying condition.
I think a far more likely story is just that Curatolo was extremely vulnerable to "suggestions" or coercion by the police that he come forward with some kind of story placing Knox and Sollecito outside their house at a particular time.
My first response to your post above only addressed the hallucination angle. But reading it again this morning prompted another thought about Curatolo - one that's been discussed here before, but which merits revisiting.
I believe it's highly possible that Curatolo was essentially under the control of the Perugia police in November 2007 (and long before and long after that time). I think the evidence to support that assertion revolves around his subsequent drug-dealing arrest and conviction. As far as can be ascertained,
the allegations that led to his conviction dated from 2004. If so, then the fact that he was not even arrested for the offences until January 2011 has to raise serious questions. And the questions become even more pressing when it appears that the police had cast-iron evidence of Curatolo's criminal offences in the form of video recordings of him dealing, and (most likely, based on the known evidence) a police plant/informant who actually bought the heroin from him. And the police would have had all this evidence in their hands way back in 2004.
Therefore, the most obvious - and damning - question is this:
if the police had such hard evidence of Curatolo's heroin dealing in 2004, why was he not arrested and prosecuted until 2011? And the only answer that makes any sense whatsoever is that the police/prosecutors deliberately and consciously decided not to arrest/prosecute Curatolo for some reason.
So the next question would be: why would they decide to hold back on arresting/prosecuting Curatolo? And the only reasonable answer would be this:
they wanted to hold the threat of prosecution/conviction over Curatolo in return for his agreeing to help them in some way..
So this in turn leads to the next question: how could Curatolo help the Perugia police/prosecutors to such an extent that they would be willing to hold back on pressing serious criminal charges against him? Again, I think the only reasonable answer is this:
Curatolo agreed to be a police informant on the many drug dealers operating in the vicinity of Piazza Grimana, in return for a deferment of the heroin-dealing charges.
When you stop to go through all this in a reasoned and logical manner, this appears to be one of the very few (if not the only) explanations that makes any sense. Curatolo lived in Piazza Grimana, and therefore had constant surveillance capabilities. In addition, his personal circumstances and appearance would give him excellent cover to spy upon - and report back to the police on - all the drug-dealing activities taking place in the vicinity of his park bench. I think that this is very likely to be what happened: the police/prosecutors called Curatolo in for a "polite chat" some time in late 2004; they presented him with the evidence of his heroin-dealing activities; they then told him that they would be willing to hold back on arresting and charging him, so long as he agreed to be a police informant in the war on organised drug gangs.
I think that a person in Curatolo's position would jump at the chance to take such a deal. I think that it made him beholden to the police/prosecutors in many ways. And I think it leads directly to the last link in the puzzle:
By November 2007, Curatolo would have been acting as an informant for some three years (according to my theory). It's likely that his usefulness to the police/prosecutors could have been waning, and/or that they were finding out that he was an unreliable/incompetent informant, partly owing to his continued use of heroin. So when the Meredith Kercher murder occurred, I think it's very possible that the police/prosecutors had another "friendly chat" with Curatolo. I think that in this conversation, they could have told him that they now wanted his assistance in the murder investigation. I think they could again have used the drug charges as currency, in order to "persuade" Curatolo to "remember" seeing Knox and Sollecito on the night of the murder. Essentally, the police/prosecutors could have said something along the following lines to Curatolo:
"Agree to become a prosecution witness against Knox and Sollecito, or we'll arrest and charge you immediately on the heroin-dealing charges."
I think that
this is how Curatolo came to be in the witness box in Massei's court, with his ludicrously inept and contradictory tale of seeing Knox and Sollecito on the evening/night of November 1st/2nd 2007. I further think that the police/prosecutors realised that Curatolo had made a terrible witness, and it's also possible that news of the police/prosecutor knowledge of his heroin dealing way back in 2004 had somehow come to light (maybe through a leak, or through defence investigations in advance of the appeal). I think that by January 2011 the police and prosecutors therefore decided that they had no option but to pull Curatolo in on these heroin-dealing charges.
