Police and prosecutors are faced with a difficult task when a stalker faces arrest for sending threatening letters or displaying other harassing behaviors. They must make a compelling case for a posed threat. In this article, expert testimony is discussed as having the potential to provide an assessment to convince a judge of dangerousness under a clear standard of proof. A well-prepared expert witness can testify to the past behavior of the defendant and offer an opinion as to the potential to engage in future violence. The FBI’s National Center for the Analysis of Violent Crime (NCAVC) offers a resource to law enforcement for the evaluation of such threats and assessment as to the risk of violence. The NCAVC reviews specific crimes from behavioral, forensic, and investigative perspectives. The NCAVC consults on matters of stalking when asked to conduct a threat assessment, render an opinion on the potential risk of violence, or provide investigative strategies. Two cases are presented illustrating how the NCAVC assist prosecutors by providing expert testimony, thereby convincing judges that the offender poses a risk to the victims.