That's not really true, you can place someone under citizen's arrest. You can, sure. However, practically speaking if you're performing a citizen's arrest without using force, he's pretty much free to flip the bird at you and walk away. If you chase him down and restrain him, you're almost definitely getting assault charges if you're just a regular citizen... mall cops and such probably get additional courtesy. At least, that's how I understand it works in metro areas.    Some further research indicates that CA citizen's arrests are only applicable to felonies, and given that most simple theft is a misdemeanor, we probably can't arrest for it:  http://www.criminalattorney.com/page...ens_arrest.htm     If, however, the prosecutor doesn't file charges, or even if he does, you could still be sued for false arrest, or if you don't have enough evidence, charges could be filed against you.  It's not an issue of it being illegal, just highly inadvisable. True, there is that too. For my reason above, I more or less forget about citizen's arrest as an option, unless you're in a position where you're close to or at the point of being able to justify lethal force.