Can you actually make a "citizen's arrest" in Las Vegas?
Yes. The law is very clear. NRS 171.126 provides that any citizen can arrest a person for a misdemeanor (or larger offense) committed in their presence or any felony whether it is witnessed or not, as long as there's reasonable cause to believe the person did the crime. In making the arrest, the person can't use any more force than is necessary and reasonable under the circumstances — and certainly not deadly force unless it's in self-defense.
How does it work? That's the tricky part. There are no clear guidelines as to how to conduct a citizen's arrest, and when it has been used, it's usually just detaining the person until the police arrive.And if the suspect flees? NRS 171.134 says “the person from whose custody he or she escaped … may immediately pursue and retake the person at any time and in any place within the state.”
Is there a downside? The obvious concern involves the person who's not happy to be citizen-arrested and gets physical. Also, what if the citizen is wrong? The person arrested could sue for things like false imprisonment or assault with a deadly weapon (if you use one to detain the person). The better course is the obvious one: Get as much information as you can and relay it to cops.