A bomb planted by a maintenance worker at an equestrian centre in Benton, Louisiana sent the owners flying in the air Saturday but were not injured.

"We think it was our Christmas miracle," Tracy Hewlett told the Associated Press.

She and her husband Bobby are the owners of the 280-acre Holly Hill Farm Equestrian Center, which has three houses and a couple of bunkhouses.

Maintenance worker Douglas Holley, 54, was arrested and charged with capital murder and making a bomb after he placed the explosive below the couple's bed.

The couple's three small dogs and a cat which were with them on the bed were also unscratched.

They think Holley is mentally ill and feel sorry for him.

"He's just ruined his life," she said.

The couple returned from a trip to Australia Friday and woke up at 3:30 a.m. Then they heard an explosion.

"There was a big flash of light, and both of us went flying. My husband flew over the top of me onto the floor by my side," she said.

The explosion knocked books from shelves in the living room and pictures from walls in several rooms. Neighbours half a mile away said the blast woke them up.

They called 911 thinking that it was a gas leak. Police started investigating about disgruntled employees, upset clients or enemies.

When the couple were asked if they knew anyone who could put the bomb inside their house, they said it was Holley, who came to the centre four years ago and has lived there for three years, she said.

"We had never had any problem with him. But he's a bit of a loner, very anti-government, never wanted to work with anybody. He had been estranged from his family. But besides that, he's a likeable guy that everybody here got along with," she said.

The Bossier Parish Sheriff's Office said a search of Holley's residence revealed materials for making explosive devices and evidence that he researched bomb-making information.

"He knew where they were and where they would be," said Lt. Bill Davis, sheriff's office spokesman.

Jail records show that he was being held without bond on two counts of attempted first-degree murder and other charges including a Caddo Parish court warrant from 2009 on letting cats and big dogs roam at large.

She said the only problem they had with Holley was that her husband failed to save Holley's horse in the summer. The horse was euthanised.

Hewlett added that other employees said Holley "said some odd things to them. Just all this anti-government stuff, something about witchcraft. Really bizarre things."

The blast left a basketball-sized hole on the floor.