From wikipedia:

"The FBI closed its file on December 31, 1979, after a 17-year investigation.[7] Their official finding was that the prisoners most likely drowned in the cold waters of the bay while attempting to reach Angel Island, it being unlikely that they made it the 1.25 miles to shore due to the strong ocean currents and the cold sea water temperatures ranging between 50 and 55 degrees Fahrenheit. They believe the remnants of the raft and the wallet wrapped in plastic containing personal effects of the Anglins, was indicative that the raft had broken up and sank after being launched from Alcatraz, and that the three convicts had tried to swim for it, before succumbing to hypothermia, and their bodies were swept out to sea by the strong current in San Francisco Bay.[2][3][5][11] The U.S. Marshals Service investigation remains open, however. As Deputy U.S. Marshal Michael Dyke told NPR in 2009: "There's an active warrant, and the Marshals Service doesn't give up looking for people."[49] Dyke also pointed out that the bodies of two out of every three people who go missing in San Francisco Bay are eventually recovered.[34]"