Man, this is a sticky controversial issue - not just surrounding the earthquake, but in science generally.
TL;DR
* The scientists may have been completely culpable
* The scientists may have been completely scapegoated
* The truth may be anywhere inbetween
* We don't have anywhere near enough information to judge
Rant:
The problem is that we're in no position to judge really without knowing a lot more of the detail surrounding the case. Risk is a hideously complicated issue, both from the point of data collection and analysis, through balanced and non-partisan communication, to appropriate response and management. There are so many places where responsibility could be placed in something like this.
Risk is fundamentally broken down into different scopes: assessment, communication and management (the wording is sometimes different, but the scope is broadly the same). Within each of these come different responsibilities that are effectively assigned on a case by case basis, normally based on policy, sociology, politics, and moral philosophy. I was going to go into this in a bit more detail, but frankly it would be 20 pages long and it's already out there in the published literature, so I won't waste people's time. Instead, I'll throw out some questions and some food for thought:
Should there be a distinct separation between those assessing what the risks might be, and those responsible for acting on them? Should the communication be carried out by data analysing nerds or PR professionals? Should the communication be tailored for people with a given level of expertise, and should it be targetted at the general public or those with the authority to act on the risk assessment? Should the risk assessment be deterministic or probabilistic? Should the risk management be carried out by local politicians or governed by national policy? What justifications need to be in place for various levels of policy to be implemented?
There are plenty of arguments for pretty much every combination of the above, but the bottom line is the responsibility when things go wrong is decided by the policies that govern who would bear that responsibility, on the basis of those individtuals not correctly performing their roles to the expected standard. If, for example, the scientists were told that their job was to write a full risk impact assessment for each of the potential outcomes, with an indication of how likely each was, and the outcome in question they wrote as "very unlikely, no precaution is warranted", then it could be argued that they failed in their duty, with the consequence that people lost their lives. If they were told not to make any comment on the appropriateness of a given action (as is often the case with scientists in a strictly risk assessment role), and they publicly signed off on a press release saying that precaution against this event was not warranted, a case could be made for malpractice.
Stepping back from the implementation of policies, there are more issues underlying how conclusions were reached in the first place:
Did the scientists properly assess the data supporting any statements or conclusions that they may have made? If not, was the fault theirs? Or an oversight committee's? Or a case of scientists insufficiently competent being poorly assigned their roles? Was the communication in line with the assessment, or did it underestimate the risk disproportionately? If so, was this the fault of the risk assessors not making sure the risk communicators understood the situation well enough to communicate accurately? Was there supposed to be a check by the risk assessors to make sure all information communicated to the public accurately matched the estimated risks, and was this omitted from the process?
It's easy to try to take an arbitrary soapbox about how terrible this is for science, but to compress an incredibly complex situation into "guilty for failing to predict earthquakes" does a gross injustice to just how complicated risk is. It also undermines the fact that there are chains of responsibility built into any process, and it's quite possible for individuals to be found responsible in situations where there jobs were not performed adequately - if that failure leads to deaths, then a charge of manslaughter seems feasible. It's also possible that these scientists really were completely scapegoated, but we really have no way of telling from the information we have available. We just have to hope that the Italian judiciary system had enough evidence to judge based on as complete a picture as possible (and, really, as complete a picture as is normally required for a criminal charge).
EDIT: Caveat