ALCATRAZ ISLAND, Calif. - 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 inmates: murderers, mobsters, and 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," said Johnson, 38. Holding a bunch of keys, he cautiously makes his moonlit rounds across the island.

He walks the old cell blocks 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.

"This is one creepy place after dark," he said. "It can make the hair on the back of your neck stand up straight."

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.

Officers watch both the ferry docks and federal facilities, mindful of pranksters or protesters. American Indians fighting for civil rights once occupied Alcatraz for 19 months, starting in November 1969.

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.' "

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, "like in that Alfred Hitchcock film, The Birds."

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

The last rays of sun gone, the island fortress becomes a grim, humorless place, the stuff of black-and-white 1950s crime photos. Johnson plays upbeat music on his iPod.

He earns overtime pay for his 18-hour shifts (3 p.m. to 9 a.m.), but sometimes, in the dead of night, he says, "It seems like blood money."

At 8 p.m., his radio squawking with park police chatter, Johnson winds his way up a switchback as birds dive-bomb from ledges. The cell house looms like a haunted castle.

He walks cell-block rows that inmates nicknamed Broadway, Sunset Alley and Seedy Street. He enters a solitary cell, its heavy iron door creaking. The tiny quarters remain perfectly black even after his eyes grow accustomed to the space.

He stops at the cell of Frank Lee Morris, whose daring breakout was immortalized in the film Escape from Alcatraz. Morris and two others left dummy heads fashioned out of soap and toilet paper inside their cells. The idea was to fool guards while they left through holes chiseled in cell walls.

Johnson looks at a model of one fake head left in the cell as a tourist display. He knows how the men felt: "Ten years here? I'd go crazy before that."

By dawn, the night watchman is weary of the Rock. Passing the keys to a ranger, he makes his own escape from Alcatraz, the sun on his face.