Before revision: In the United States federal system, conspiracy to commit a crime in itself constitutes a crime, so an arrest for it would not be preemptive... nor would the arrest be preemptive since by definition preemptive arrests occur before a crimeis committed.
After revision: This practice is distinct from an arrest on a charge of conspiracy to commit a crime in itself constitutes a crime, so an arrest for it would not be preemptive... nor would the arrest be preemptive since by definition preemptive arrests occur before a crimeis committed.