HESSTON, Kan. — A little more than two hours into his painting shift at the Excel Industries plant here, Matt Jarrell’s co-worker Cedric Ford was nowhere to be found. Mr. Ford was one of Mr. Jarrell’s best friends on the job; that day, he had promised to help Mr. Ford remove a rusty screw from the old gray Nissan pickup truck he had recently bought.

When another employee stepped in to relieve him, Mr. Jarrell went out to the parking lot and saw Mr. Ford roll up in a different truck that screeched to a halt. Mr. Jarrell recalled that his friend hopped out holding a rifle, shot a person in front of him, then ran into the factory and kept shooting.

Michael P. Dellinger looked up in the direction of the pop-pop-pop noise and saw Mr. Ford “just standing there with a rifle,” he said. “It took me a second to realize. He just kept shooting. I grabbed a guy standing next to me and said, ‘We got to go.’ ”

As the authorities piece together what led Mr. Ford, 38, to fatally shoot three of his colleagues and injure 14 more on Thursday, the latest in a long string of mass shootings, starkly contradictory pictures of him have emerged. Stunned friends and co-workers described a gregarious yet quiet man, a steady worker who glowed about his children — more subdued in recent weeks, but giving no hint of the mayhem to come.