INDIANAPOLIS -- The family of a construction worker killed Wednesday at the site of the Indiana Convention Center expansion said they plan to sue.

Stanley Roberts, 55, an ironworker with Harmon Steel Inc., was killed Wednesday when he fell 50 feet from a mechanical lift while working on an iron girder. Officials at the scene said Roberts was wearing a safety harness, but that it wasn't attached to anything.

The family's attorney, John Daly, said preliminary information suggests that a hole in the ground may have caused the mechanical lift to flip. He said the general contractor, excavators and safety inspectors are responsible for making sure the ground is level.

"It was wide enough and deep enough that when the wheels on the lift hit, it actually caused the wheels to tip," he told 6News' Sarah Conrell. "I think there is plenty of responsibility to go around."

Work at the site has been shut down since Roberts' death as inspectors with the Indiana Occupational Safety and Health Administration complete their investigation.

A spokesman for the construction project said that he would reserve comment on any legal action until that process is complete, which could take several weeks.

Stanley Robert's wife, Kathy Roberts, said she is in a state of disbelief, remembering her husband of 27 years.

"I'm going to miss him so much. I already do," she told Cornell Wednesday night. "I keep waiting for his truck to pull up in the yard."