HOUSTON - Federal investigators on Saturday began trying to figure out why one of the world's largest mobile cranes toppled over, killing four contract workers and injuring seven others.

Officials said it could take awhile to find out what caused the 30-story-tall crane to collapse Friday at a LyondellBasell refinery in Houston, the latest of several deadly crane accidents around the country.

The massive crane, capable of lifting 1 million pounds, was owned by Deep South Crane & Rigging, which Saturday released the names of its four workers killed in the accident.

"We wish we had all of the answers on what happened and why -- but we do not -- and speculating on cause would not resolve anything," the company said in a statement. "But we are actively working to find those answers."

The four men killed were Marion "Scooter" Hubert Odom III, 41, of Highlands; John D. Henry, 33, of Dayton; Daniel "DJ" Lee Johnson, 30, of Dayton; and Rocky Dale Strength, 30, of Santa Fe, Texas.

At the LyondellBasell refinery, company officials said they were trying to restore normalcy. The refinery brought in grief counselors and will hold a series of safety meetings to address concerns about the accident starting Monday, said David Roznowski, a company spokesman.

"This is a real blow to our refinery team, and it will take some time to recover from this," he said.

Investigators with the Occupational Safety and Health Administration began their formal accident investigation early Saturday, Roznowski said.

Two of the injured workers remained in Houston hospitals Saturday. Their injuries were not life-threatening, Roznowski said.