U.S. government organizations, including the FBI, had been monitoring Cuban spy activities for over 30 years, but made only occasional arrests. However, after the two Brothers to the Rescue aircraft were shot down by Cuban MiGs in February 1996 and four U.S. citizens were killed, on the basis of information sent to Cuba by an infiltrator of the group, the Clinton administration launched a crackdown. According to U.S. attorney José Pertierra, who acts for the Venezuelan government in its attempts to extradite Luis Posada Carriles, the crackdown was aided by the cooperation of the Cuban authorities with the FBI in 1997. The Cubans provided 175 pages of documents to FBI agents investigating Posada Carriles's role in the 1997 bombings in Havana, but the FBI failed to use the evidence to follow up on Posada. Instead, they used it to uncover the spy network that included the Cuban Five. According to FBI evidence at the trial, the FBI had been monitoring the communications of Hernández, whose information enabled the shootdown, for several years prior to that event. He was not arrested until 1998.