If it's so normal to hire a serial killer from the dark web, why don't the FBI just capture them all?

Like why wait till they commit a crime to capture them? When they literally have their emails on display with the prices on the dark web!
If it's so normal to hire a serial killer from the dark web, why don't the FBI just capture them all?
If it's so normal to hire a serial killer from the dark web, why don't the FBI just capture them all?
If it's so normal to hire a serial killer from the dark web, why don't the FBI just capture them all?
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