Hundreds of leads were pursued by the Federal Bureau of Investigation (FBI) and local law enforcement officials in the ensuing years, but no conclusive evidence has ever surfaced favoring the success or failure of the attempt.

[5] In 1979 the FBI officially concluded, on the basis of circumstantial evidence and a preponderance of expert opinion, that the men drowned in the frigid waters of San Francisco Bay without reaching the mainland.

Clarence and John were reportedly inseparable as youngsters; they became skilled swimmers, and amazed their siblings by swimming in the frigid waters of Lake Michigan as ice still floated on its surface.

[23] Over the subsequent six months, they widened the ventilation ducts beneath their sinks using discarded saw blades found on the prison grounds, metal spoons from the mess hall, and an electric drill improvised from the motor of a vacuum cleaner.

[24] The men concealed their work with painted cardboard, and masked the noise with Morris's accordion on top of the ambient din of music hour.

[22][23] Once the holes were wide enough to pass through, the men accessed the unguarded utility corridor directly behind their cells' tier and climbed to the vacant top level of the cellblock, where they set up a clandestine workshop.

[25] They also assembled a six-by-fourteen-foot rubber raft, the seams carefully stitched by hand and sealed with liquid plastic available in the shops,[25] and heat from nearby steam pipes.

[22][23] The men concealed their absence while working outside their cells, and after the escape itself, by sculpting dummy heads from a hand-made papier-mâché-like mixture of soap, toothpaste, concrete dust, and toilet paper, and giving them a realistic appearance with paint from the maintenance shop and hair from the barbershop floor.

At the northeast shoreline, near the power plant—a blind spot in the prison's network of searchlights and gun towers—they inflated their raft with a concertina stolen from another inmate and modified to serve as a bellows.

On the same day and in the same general location, workers on another boat found a wallet wrapped in plastic complete with names, addresses, and photos of the Anglins' friends and relatives.

[33] On July 17, a month after the escape, a Norwegian ship, SS Norefjell, spotted a body floating in the ocean 15 nautical miles (28 km; 17 mi) from the Golden Gate Bridge.

[35][36] FBI investigators announced their official position that, while it was theoretically possible for the men to have reached Angel Island, the odds of them having survived the turbulent currents and frigid waters of the bay were negligible.

"[51] In 1989, a woman who identified herself only as "Cathy" called Unsolved Mysteries tip line to report that a photo of Clarence Anglin matched the description of a man who lived on a farm near Marianna, Florida.

[54] A day after the escape, a man claiming to be John Anglin called a lawyer, Eugenia MacGowan, in San Francisco to arrange a meeting with the U.S.

[56][57] In 1993, a former Alcatraz inmate named Thomas Kent told the television program America's Most Wanted that he had helped plan the escape, and claimed to have provided "significant new leads" to investigators.

[59] A 2003 MythBusters episode[60] on the Discovery Channel tested the feasibility of an escape from the island aboard a raft constructed with the same materials and tools available to the inmates, and concluded that it was "possible".

Furthermore, a 1955 blue Chevrolet (California license plate KPB076) was reported stolen in Marin County the same day—a claim corroborated by contemporaneous stories in the Humboldt Times and the San Francisco Examiner.

[65] A 2014 study of the ocean currents by scientists at Delft University concluded that if the prisoners left Alcatraz at 11:30 p.m. on June 11, they could have made it to Horseshoe Bay, just north of the Golden Gate Bridge, and that any debris would have floated in the direction of Angel Island, consistent with where the paddle and belongings were actually found.

[66][67] A 2015 History Channel documentary entitled Alcatraz: Search for the Truth presented further circumstantial evidence gathered over the years by the Anglin family.

[68] Kenneth and David Widner displayed Christmas cards containing the Anglins' handwriting, and allegedly received by family members for three years after the escape.

Michael Dyke, the last Deputy Marshal assigned to the case, said Brizzi was "a drug smuggler and a con man," and was suspicious of his account.

Dyke said measurements of the physical characteristics of the Anglin brothers indicate that they are not the men in the Brazil photo, but he acknowledged the difficulty in making a definitive determination and ruling it out as a valid lead.

[73] In January 2020, an Irish creative agency and AI specialists at Identv used facial recognition techniques to conclude that the men in the photo were John and Clarence Anglin.

Surviving family members, who said they have heard nothing since Robert lost contact with the brothers in 1987, announced plans to travel to Brazil to conduct a personal search; but Roderick cautioned that they could be arrested by Brazilian authorities because the Alcatraz escape remains an open Interpol case.

[69] In 2018, the FBI confirmed the existence of a letter, allegedly written by John Anglin and received by the San Francisco Police Department in 2013.

[77] In a 2019 episode of the series Mission Declassified, investigative journalist Christof Putzel corroborated much of the information released by the FBI and other sources, including the raft found on Angel Island.

[82] The escape was shown in a two-part 1980 TV movie Alcatraz: The Whole Shocking Story, which starred Ed Lauter as Morris, and Louis Giambalvo and Antony Ponzini as the Anglins.

[citation needed] The film Dear Eleanor (2016) starring Liana Liberato, Isabelle Fuhrman and Jessica Alba, features Frank Morris, played by Josh Lucas.

Set in 1962, in the backdrop of the Cuban Missile Crisis, the main characters form a friendship with a recently-escaped Morris during their cross-country trip to meet Eleanor Roosevelt and help him evade the police before fleeing the country.

In season 2 of Loki, it is revealed that recurring character Casey, played by Eugene Cordero, is a temporal variant of Frank Morris.