ATLANTA  — Federal investigators were working through the weekend to start determining what caused a pedestrian bridge being built high above an Atlanta park to collapse, killing one man and leaving 11 other workers hospitalized, seven in intensive care.

Contractors were pouring concrete on the "canopy walk" at the Atlanta Botanical Garden when it crumbled Friday morning, sending workers hurtling up to 40 feet to the forest below. The U.S. Department of Labor's Occupational Safety and Health Administration was investigating Saturday, but spokesman Mike Wald said it could take months to determine what happened.

The 30-acre garden, which is adjacent to Atlanta's popular Piedmont Park north of downtown, will stay closed through the weekend out of respect for the workers and their families, according to a statement on the Garden's Web site. It is set to reopen Monday.

The Web site describes the collapsed skyway as the "only canopy level pathway of its kind in the U.S." Rising to four stories high, it was to be supported by a system of cable wires "designed to hold the structure firm and steady without impacting tree roots."

Meanwhile, Hardin Construction, the contractor for the project, has held meetings about how and if the bridge building would continue, said company spokeswoman Barkley Russell.

"Our focus continues to be with the workers and their families and we are offering continuing support and assistance," Russell said in an e-mailed statement.

Killed in the collapse was 66-year-old Angel Chupin of Marietta, according to the Fulton County Medical Examiner's Office. Eighteen men were injured. Of the 16 treated at Grady Memorial Hospital, five had been discharged by midday Saturday. Two others were treated and released at another hospital.

Grady spokeswoman Frankie Smith declined to release the conditions of the 11 still hospitalized, but some had suffered serious head and spinal injuries. Smith said the remaining patients and their families did not want to do any media interviews over the weekend.

Hardin's spokeswoman Russell also addressed media reports that Hardin had received three OSHA safety citations.

"The three citations mentioned in the media span a 10-year period in which Hardin has completed over 50 million square feet of space and over 250 projects," the statement says.

The statement said all contractors on the garden project attend weekly safety meetings.