An Apple ID and iTunes purchases have helped investigators find and arrest Artem Vaulin, the alleged owner of KickassTorrents (KAT). The U.S. government apparently identified an iCloud email address belonging to Vaulin, and sought a court order compelling Apple to offer iTunes purchase activity for that address.

Apple ID, iTunes purchases lead to arrest of alleged torrent site owner

From the government's complaint against Vaulin (via TorrentFreak):

Records provided by Apple showed that conducted an iTunes transaction using IP Address on or about July 31, 2015. The same IP Address was used on the same day to login into the KAT Facebook Account. Then, on or about December 9, 2015, used IP Address to conduct another iTunes transaction. The same IP Address was logged as accessing the KAT Facebook Account on or about December 4, 2015.

Vaulin has been charged with conspiracy to commit criminal copyright infringement, conspiracy to commit money laundering, and two counts of criminal copyright infringement. In addition to Vaulin's arrest, the KickAssTorrents domain was seized by authorities. Until that point, KAT was the largest torrent site in the world.