David Talmage, a social worker with an office near Lakeview Regional Medical Center just north of Mandeville, was in his office with a client when he heard a loud bang Monday just after 11 a.m.

With monsoon-like conditions outside, Talmage thought a transformer had blown.

But his client, a former member of the military, knew better.

“He thought it was gunfire,” Talmage said Monday afternoon.

That shot, and a second one moments later, sparked a manhunt Monday afternoon for the shooter, who apparently squeezed off two shotgun rounds from a stand of trees near the hospital and then disappeared, leaving only a single shell as evidence.

Witnesses said they saw a heavyset white man wearing heavy clothing, according to St. Tammany Parish Sheriff Jack Strain.

Deputies, aided by State Police, Mandeville police and federal agents, scoured the area around the hospital throughout the afternoon. They searched buildings and vehicles in an effort to locate the shooter.

The hospital, which was put on lockdown moments after the shots were fired, returned to normal operations in short order.

The shooter did not appear to be targeting anyone or anything — Strain said the first shot appeared to have been fired into the ground — and no injuries were reported.

Witnesses reported seeing the man step out from the trees that line the north side of a road on the hospital’s northwest side. They said he unwrapped the gun, perhaps from a blanket or a towel, before firing the shots. When he was done, he walked along the trees that line the road until he came to the U.S. 190 service road, where he turned north, still on foot. That was the last reported sighting of the man, officials said.

Strain said deputies weren’t sure if the shooter had gotten into a car or remained on foot.

Law enforcement officers blanketed the area, some with dogs and others carrying assault-style rifles. About 1:30 p.m., a tip led a stream of deputies to head north to an area near Copeland’s restaurant. But the tip didn’t pan out, said Capt. George Bonnett, a spokesman for Strain, and after that the trail went cold.

Strain encouraged anyone who has any information or sees someone carrying a long object wrapped in a towel or a blanket to call 911.

James Klein, a psychologist with an office near Talmage’s, called patients who had appointments scheduled Monday to let them know they could cancel if they wished.

“It’s like something you read about or hear about somewhere else,” he said. “It was surreal.”

Staff writers Sara Pagones and Matt Sledge contributed to this report. Follow Faimon A. Roberts III on Twitter, @faimon. Follow Sara Pagones on Twitter, @spagonesadvocat.