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A safety measure built into Taser stun guns helped lead Milwaukee police to the robbers.

When a Taser is fired, it releases tiny bits of uniquely numbered confetti that correlate to the specific weapon.

It can then allow Taser International to track the sale of the specific weapon, which could lead police to the buyer, assuming the Taser wasn't passed between too many other people before its use.

You can see the tracer confetti being released in this slow motion video of a Taser being fired.

Taser calls the system "Anti-Felon Identification," or AFID. It is meant to deter people from using the Taser to commit a crime.