[gwillen]

Shopkeepers have the legal power to detain shoplifters in most US jurisdictions. They've just historically (in the modern era) been too afraid to use it.

[AlbertCory]

I thought of that after writing that.

A lot of legal questions come down to a game of chicken, unfortunately. Who is willing to bear the most risk?

Maybe if it really was shoplifting, it goes more like this:

Guard: Wait right here, please.

S: Am I under arrest?

Guard: You are being detained until the police arrive. What is your name?

S: Oh, I'm detained? Funny, I don't notice any cuffs. So I think I'll leave now (drops goods & hops on bike).

Guard: (ponders: If I tackle him, what happens?) Calls police.

Now what?