An employee (A) said she walked in on a conversation in the lunch room where a group of employees (B) were saying that employee (C) said she was so frustrated and was going to kill employee (A). Employee (A) says she now feels that her life is threatened and so is her familys life. Employees (B) all say that the employee (C) was not serious and it's similar to when people say "Im going to poke my eye out, or something to that effect... just venting frustration. Employee (A) and Employee (C) have never gotten along and everyone believes they are both trying to get the other person fired. What do I need to do immediately? Employee A and C work in two different offices and they only see each other twice a month on saturdays. Do I need to involve police and/or labor lawyers? Everyone believes employee A is being dramatic and using this as an excuse to get rid of employee C. This incident supposedly happened over a month ago and employee A just brought it up yesterday, after she was reprimanded for speaking about employee C negatively. We are a doctors office and do not have an HR dept.

It was already handled by the powers that be with a reprimand, so why would you seek to take it further? What's your position in the pecking order of authority? If I was in charge, I would tell them both to stop the personal bickering on company time or face discipline, or DISCHARGE.

Maybe change Saturdays schedule to keep these loons apart?

I like talanimans approach on this... schedule them to keep them apart, and cool off and then if they can't learn to play nice with each other... get rid of both. What this isn't, is a 3rd party's business.. unless the third party is the employer, supervisor or HR rep. Anyone else needs to mind their own business.

Also, its not just actual words... CONTEXT means everything. Maybe 1% or less of people who ever say that would EVER actually even consider attempting it.

1. "What do I need to do immediately"

Infers you are in a management position. So, what exactly is your position with the company? Do you supervise either of these 2 people? Who did the reprimanding?

I am the practice manager and supervise both the clinical and reception staff. Employee A was reprimanded (by the physician) about the bad mouthing Employee C when I was not in the office (on a weekend shift). By reprimanded, I mean talked to about how that is not acceptable.

I can easily keep them apart going forward as they only see each other every other month. I just wanted opinions because the word KILL was used. I don't want to take it too lightly and say stop bickering because in the completely off chance something did happen it would look like we didn't do anything to help an employee and had her in an environment where she didn't feel safe.

You don't need to involve the police because they won't be involved. 99.9% of all threats are just heated words, fortunately, and the police need actions (or possibly repeated and really creepy threats) to look into it. Threats fall under free speech.
You can pay a labor lawyer if you wish, but I wouldn't bother.
What I would do is call A and C in one at a time, say that both their behaviors are going in their files, that they are on probation for 60 days, and that if they continue to disrupt the flow of the offices, both will be let go. That includes involving everyone else.
If you have different company policy, use it. If you don't, WRITE a personnel handbook.
You need to bring them in for formal reprimand because the doctor already reprimanded one of them. The cat's out of the bag, so to speak, legally.
But legally, neither one of them has a case against the company for unsafe environment or unfair firing.
Many companies have a multi-step process for warning, probation(s), and firing. Every one of them is recorded with details of incidents. Just the fact that they fight with each other is grounds for firing, because they should be working. I would tell them that.

Thank you all for the feedback I really appreciate it!