Alberto was detained by Pinochet's thugs in 1973. They recruited him as an active collaborator; he worked in a couple of Pinochet's prison facilities.
On January 10th, 1975, he disappeared.
Four days later, he was found floating in the sea on Las Cruces beach, tied with wires. He was apparently last seen alive at the Tejas Verdes military compound. The investigation was dismissed because there was, they said, no proof that he'd died due to a crime. Sure, he'd been tied up with wires and dropped in the ocean - but that sort of thing was LEGAL under Pinochet.
Bet you didn't know that Pinochet sometimes offered free helicopter rides for his COLLABORATORS. Now you do.