The statistical implication of the full record is that escaping from Alcatraz was not entirely impossible — it happened, repeatedly, in the sense of leaving the island’s immediate perimeter. What was difficult, by the evidence, was making a successful mainland landing and evading recapture. Of the thirty-six who attempted, twenty-three were caught. The majority of those who were not caught are accounted for by shooting and confirmed drowning. The five listed as missing, presumed drowned — including the three from June 1962 — are the statistical residual.
Whether that residual represents successful evasion or simply bodies not recovered is exactly the question the evidence does not resolve.
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## The Equipment They Left Behind: A Physical Inventory
The workshop on the top tier of the cellblock was searched by investigators on June 12 and in the days following. What was found there, and what was not found, is part of the documentary record.
The workshop contained materials consistent with an extended manufacturing operation. Needle and thread used for the raft and life vest construction. Liquid plastic sealant. Remaining pieces of raincoat rubber not incorporated into finished equipment. Cardboard and paint consistent with the concealment panels. The unfinished pontoon — a component of what would have been a larger flotation system if the escape had waited longer. Three life preservers for the original four participants. Equipment for the fourth man who did not leave.
What was not in the workshop: the main raft, three life preservers (the ones that went into the water), paddles. These had been taken. The fact that the men carried the raft to the water — rather than leaving it in the workshop and testing whether they could build a new one on shore — demonstrates confidence in their construction.