Since the Tarasoff case of 1976, mental health professionals are recognized to have a "duty to protect" third-party targets from violence-threatening patients, but little is known about what happens after clinicians warn law enforcement. In 2000, Huber et al. published a study that surveyed Michigan police about "Tarasoff warnings." We conducted a 20-year follow-up study, inviting all Michigan police and sheriff departments to participate. There were no significant differences between studies about knowledge of Tarasoff-related policies, which was low in both surveys. We found significant decreases in the number of officers who had ever intervened due to warning calls. Of the survey respondents, 83% supported documenting warning calls. For those who received warnings, 96% followed up with at least one intervention. In both studies, notifying other officers was the most common action taken. 56% said they would take action to remove a firearm. We identified opportunities for training law enforcement.