Though Alcatraz is now a tourist stop, the barren outpost still holds the power to test the sanity of those paid to patrol it at night.

Each day at sundown, when the last tour boat departs this desolate, wind-swept outpost, one lonesome soul is left behind. He's the night watchman of Alcatraz.

Guided by the beam of his flashlight, Gregory Johnson inches down the gloomy infirmary ward of this retired prison, once home to the nation's most malicious killers and psychotic criminal malcontents.

"Hey, what's that noise?" he asks, throwing the light against the half-open door of a solitary confinement cell.

He pauses, shrugging off another unexplained Alcatraz phenomenon.

"Man," he whispers, "I couldn't imagine being out here at night without my gun."

Until the first boat arrives after dawn, the U.S. park police officer spends the night battling both his nerves and imagination, patrolling the place once known as America's Devil's Island.

Over the years, Alcatraz was the dreaded last stop for 1,576 murderers, mobsters, the nation's most-wanted crooks.

Known as "the Rock," the 12-acre penal island was notorious for cramped cells and rigid discipline that at times demanded silence. Decades after the prison closed March 21, 1963, with inmate Frank Weatherman's valediction, "Alcatraz was never no good for nobody," all that remains is the lore of the desperate men once locked up here.

"I don't believe in ghosts, per se," says Johnson, 38. Holding a shackle of keys, he cautiously makes his moonlit rounds across the island.

He walks the old cellblocks that once housed bank robber and gangster Arthur (Doc) Barker and kidnapper Alvin (Creepy Karpis) Karpavicz, a former Public Enemy No. 1.

He checks the medical ward where Robert Stroud (the Birdman of Alcatraz) spent 17 years.

He peers into the laundry room where Chicago mobster Alphonse (Scarface) Capone hustled among the industrial washers.

He patrols the office of wardens nicknamed Saltwater, Gypsy, Cowboy and Promising Paul.

Now and then, the old prison plays tricks on his mind. One night, as the buoy bells clanged and the foghorn moaned, he swore he heard clinking glasses, as if a toast were being made. He hears mice skitter on cellblock floors. The wind howling often seems like crazy laughter.

For years, ferry company employees were assigned to the island's night shift. Last fall, when the National Park Service, which runs Alcatraz, changed ferry services, park police took over until the new contractor begins work this month.

Johnson initially balked at the duty he shares with other officers.

"I like to be scared, but not that scared," he said. "I had to remind myself, 'There's no one out here but me. So just put that stuff out of your mind.' "

Between 1934 and 1963, the Civil War-era military fortress turned penitentiary provided inmates with the hardest time they ever did, in part because San Francisco's cityscape reminded them of the freedom they had lost.

George DeVincenzi, a guard at Alcatraz from 1950 to 1957, said the proximity of the California culture drove prisoners nearly insane.

"Yachts circled the island, and men on the third tier of C and B blocks could see girls in bikinis drinking cocktails," he said. "It was so near, and yet so far."

The mind games got crueler.

"After dark, it got colder and danker," DeVincenzi said. "You could hear the bellow of the fog horns. It was a lonely, sometimes scary sound, even for the murderers among us."

Years after the prison shut its doors, the island's sense of seclusion remains. Until cell phones, night watchmen relied on a ship-to-shore phone to reach the mainland.

Erik Novencido worked the island night shift for 10 years. The worst part was walking inside the electroshock therapy room. Once he took a picture at night to show friends. When he developed the film, he says, the snapshot showed a face in the room staring back at him.

He never figured out what it was.

"Sometimes I was just overwhelmed by fear," he said. "The rangers told me stories about the things that happened here. And I'd say, 'Keep that to yourself. I've got my sanity to keep.' "

Veteran park ranger Craig Glassner has been afraid even during the day.

"Once on an isolated spot I heard this 'whooooo, whooooo,' like someone blowing on a big Coke bottle," he said. "I thought, 'Do I run?' Then I saw it was the wind blowing across the stanchions of a fence. It really freaked me out."

Mary McClure, who spent 12 years working nights on Alcatraz, preferred the isolation. Even so, there were strange events.

"Many times, at night in the cell house, I had the distinct sensation of being pinched on the butt," said McClure, 52, a former paramedic. "It happened with great regularity. I have no explanation for it, and I don't talk to people about it, because I know it makes me sound crazy."

John Banner, 83, spent four years as an inmate in the 1950s. He still recalls the squeal of the wind at night.

"Laying awake, listening to that wind, trying to hold on to what sanity I had left, I always thought of the brutality of that prison," said the convicted bank robber, who lives in Arizona.

When darkness comes, you don't leave Alcatraz; you flee. A ranger hands Johnson the keys to the island -- hurrying toward a ferry that whisks away the last of the day's 5,000 visitors.

Johnson stands amid the seagulls. The big birds are everywhere, lined up on walls, circling like vultures. They make him uneasy.

"It's like they're watching me, to see if I'm going to crack," he says.

He makes a sweep for any tourist stragglers and settles in for the long night.

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