NEW YORK >> Investigators are looking into the collapse of a World Trade Center scaffold that left two window washers dangling from the nation’s tallest skyscraper, 1 World Trade Center.

The workers were trapped 68 stories above the street when a cable suddenly developed slack Wednesday.

The workers held on to the teetering platform for two agonizing hours. One called his wife during the ordeal, fearful that it might be his last opportunity to speak to her.

Firefighters used diamond cutters to saw through a double-layered window and pulled the men to safety.

The dramatic rescue, coming a little more than a week after the building officially opened, was followed by throngs of New Yorkers watching from the ground and many more around the world watching on live TV.

The window washers, Juan Lizama and Juan Lopez, were working on the south side of the lower Manhattan building when one of the platform’s four cables abruptly gave way, Fire Commissioner Daniel Nigro said. The open-topped platform tilted sharply and swayed slightly between the 68th and 69th floors, he said.

“It suddenly went from horizontal to nearly vertical,” Nigro said.

Officials haven’t determined what caused the cable problem, the fire commissioner said.

It was unclear whether anything about the design of the 1,776-foot, 104-story skyscraper complicates working on the window washing scaffolds, which went into service in June.

A fire department photo shot from inside the building shows the scaffold platform hanging precipitously, with the Statue of Liberty appearing tiny in the distance.

About 100 firefighters rushed to the scene, some of them lowering ropes from the roof so the workers could secure themselves and providing a two-way radio to communicate, Nigro said. The workers, who have more than 20 years of experience between them, were harnessed to the platform, and the building’s owner said they had all the requisite safety gear and training.

After shattering the window glass, firefighters began inching another scaffold down the building as a backup rescue plan. But the workers were brought to safety through the roughly 4-by-8-foot window hole.

“It was a fairly straightforward operation,” said Battalion Chief Joseph Jardin, who oversees the fire department’s special operations.

Officials stressed that firefighters had trained for various emergencies at the tower, which is the centerpiece of the rebuilt World Trade Center.

Firefighters generally seek to cut out windows to make such rescues, but Nigro noted the trade center’s thick glass: a double-paned inner layer and an outer pane.

“And, of course, they were 68 stories up,” he said. “That presented a little bit more of a challenge.”

Lizama and Lopez were examined at a hospital and were released. Their union, Service Employees International Union Local 32BJ, said it makes sure workers follow rigorous safety protocols.

Lizama’s wife, Hilda, told the New York Post that her husband called her on his cellphone to tell her to take care of their children because “I don’t know what’s going to happen.”

She said he told her, “We’re real high. I don’t know if or how it’s going to turn out.” The Post said the couple has three sons and live in Hudson County, New Jersey.

The building’s owner, the Port Authority of New York and New Jersey, said it was suspending window cleaning there while investigating what happened.

The window washers were working for Upgrade Services Window Cleaning, which services other prominent New York skyscrapers including the nearby 4 World Trade Center.

The window washing company would only say the window washers were “doing well” after their release from the hospital. The rig’s supplier, the Tractel Group, which built and repaired scaffolds involved in two other high-profile accidents in recent years, didn’t immediately return a call seeking comment.

The Tractel Group was fined $21,000 in 2008 after a scaffold it had repaired the year before gave way with two window washers aboard while they worked on the 47th floor of an upper Manhattan building; one worker died. Tractel also built a scaffold that snapped 500 feet above the ground last June in midtown Manhattan, leaving two workers dangling; they were rescued after firefighters cut through glass.

The silvery $3.9 billion skyscraper that rose from the ashes of the Sept. 11, 2001, terror attack, opened last week to 175 employees of magazine publisher Conde Nast. Steps away are two memorial fountains built on the footprints of the decimated twin towers, a reminder of the more than 2,700 people who died in the attack.

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Associated Press writers Kiley Armstrong, Verena Dobnik, Deepti Hajela and Jennifer Peltz contributed to this report.