This chapter consists of a brief discussion on some legal aspects concerning scientists' responsibility in risk prevention processes. After proposing some introductory considerations on scientists' responsibility as such, the author deals with the L'Aquila earthquake crisis of 2009, when a strong quake destroyed significant parts of L'Aquila (Italy) and surrounding villages, killing more than 300 people. The chapter focuses on the relations between scientific knowledge, normative expectations, decision-making and criminal negligence for 'failed' risk assessment and management, paying particular attention to the role of 'regulatory science' in constructing the `reasonable person' normative standard of care in the theory of criminal negligence. This allows explaining why the first judgement in the L'Aquila trial (2012) is not convincing, having misunderstood how policy-relevant science should participate in prevention processes and the construction of normative standards. In his conclusions, the author suggests some reasons for the recent tendency to blame experts when natural or technological disasters occur.