INDIANAPOLIS -- The wife of a worker killed Wednesday at the construction site of the Indiana Convention Center expansion said she is in shock.

Stanley C. Roberts, 55, fell from a boom lift just after 3:15 p.m. at the site at 200 S. Capitol Ave., said Sgt. Paul Thompson.

Police said Roberts was working on an iron girder about 50 feet in the air when he fell out of the basket. Officials said he was wearing a safety harness, but that it wasn't attached to anything.

"The device may have been in motion and toppled. Or it's possible it was stationary and hit a soft spot and toppled over," Thompson said. "But, either way, when the device started to turn, the operator was catapulted from the device and struck the ground."

Kathy Roberts was surrounded by friends and family at the couple's east side home Wednesday night. She and her husband had been married for 22 years.

"It was just shock. I just screamed. It's still unbelievable," she told 6News' Sarah Cornell.

She said her husband had worked for Harmon Steel Inc. of Indianapolis a few years ago, and went back to work with the company six months ago.

"He's never gave me any cause of concern about the company," she said.

The Indiana Occupational Safety and Health Administration was at the construction site Thursday to investigate. Work began at the 14-acre site where the RCA Dome once stood in January, but this is the first time someone has been injured.

"Up until now, we've had a great safety record on this project," said John Klipsch of the Indiana Stadium and Convention Building Authority. "We will investigate the problem and see what happened, but we're confident it was an accident."

The site was shut down on Thursday as the investigation continues.