Step 1: Contact the police. If a company is faced with an imminent threat of violence, HR should not try to heroically neutralize the threat. No matter what the threat level, at a minimum, HR will want to get a police report on file and request increased police surveillance of the work location.
Step 2: Consider restraining orders. Let employees who have been threatened know that HR will obtain a restraining order on their behalf, but they will need to sign declarations and appear at court hearings.
Step 3: Obtain a stay-away order. If police proceed with a criminal complaint, and prosecutors file charges, HR should contact the prosecutor and request a criminal "stay-away" order in addition to the civil restraining order. This gives police more leverage and subjects the order's target to potential criminal charges for violations.
Step 4: Tighten workplace security. Survey the premises and determine what, if anything, can be done to make the workplace more secure against the potential threat. The company may need to consider installing additional security devices such as surveillance cameras or automatically locking doors, and hire security guards.
Step 5: Stay in touch with authorities. HR must make it clear to both the police and prosecutors that the company is taking the threat of violence very seriously, and is committed to seeing the civil or criminal case through to its conclusion. Law enforcement authorities are very busy. It is up to HR to ensure the case does not fall through the cracks.