[Erik]

First: Check you state laws regarding citizens arrest. Pay particular attention to the level of force allowed, and under what circumstances.

Second: Once you understand that, the issues of prudence, tactics, risk, ability, liability, etc come into play, with each instance likely being unique unto itself.

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That said, assuming you have done your homework and find yourself in a scenario such as you describe, my generic advise is to hold the person at gun point until police arrive. Issue basic, simple commands as necessary; i.e. "don't move" and "keep your hands where I can see them." Maintain available distance and cover. If the bad guy flees, let him flee.

Some will take exception to the term "hold the person at gunpoint." Fair enough. I use it to denote the portion of the encounter where a gun in hand produces the cessation of action on the bad guy's part. It ends when either the police arrive or the bad guy flees; or of course you are forced to shoot him, something outside your scenario.