Detectives are interviewing and re-interviewing people who might hold the keys to knowing why a gunman opened fire on his co-workers at an Alabama fire hydrant factory, but the answer might prove elusive, a police official said Wednesday.

Andreas Horton, 34, used a handgun to kill two co-workers at the Mueller Co. plant in Albertville and wound two others before dawn Tuesday, authorities said.

A few hours later, Horton was found dead in his vehicle in nearby Guntersville from what police said was a self-inflicted gunshot. He had parked along a road beside the cemetery where his mother was buried after dying of cancer at age 40 in 2011.

The Albertville police force’s entire detective division is working on the case and trying to learn the motive, Assistant Police Chief J.T. Cartee said Wednesday. But he said that based on his experience — and the fact that Horton is dead — people might never know why it happened.

“They’re trying to get that answer to that question that everyone wants to know — why?,” Cartee said. “We might not ever know why. That doesn’t sit well with folks but in my years of experience, I’ve learned that we don’t always get all the answers.”

Police identified the dead men as Michael Dobbins and David Horton. Police Chief Jamie Smith said that as far as he knew, the Hortons shared the same last name but were not related. All involved worked at the sprawling plant that gave the city in northwest Alabama its nickname of “Fire Hydrant Capital of the World.”

The two survivors —- Casey Sampson and Isaac Byrd — were in critical condition at a hospital in Chattanooga, Tennessee, after the shooting, Cartee said.

The hospital was unable to provide an update on their conditions Wednesday, but Byrd’s pastor told Al.com that he was undergoing surgery for extensive injuries. Pastor Glenn Randall sent a text around 4 a.m. Wednesday asking members of the congregation, Crossroads Assembly of God in Albertville, to pray for the young man.

Mueller Co., based in Cleveland, Tennessee, is a subsidiary of Atlanta-based Mueller Water Products Inc., which calls itself a leading maker of water distribution and measurement products in North America. More than 400 people work at the Albertville plant.