SPRING HILL — Brian Christopher Murphy's job was part-time but noble: Keep watch over some of Spring Hill's most vulnerable residents.

Early Thursday, for reasons that are still unclear, authorities say Murphy turned on people he was supposed to protect.

During an attack that Sheriff Al Nienhuis called "beyond brutal," Murphy used a tire jack to break most of the bones in the faces of two octogenarian residents at Atria Evergreen Woods, an assisted living facility where the 22-year-old worked as a security guard.

"Seasoned detectives said it was one of more horrific crimes that they've seen," Nienhuis said at a news conference. "It's really a miracle that they're still alive."

Miriam Lepp, 88, and Joseph Giambrone, 83, were hospitalized in guarded condition Thursday, Nienhuis said. Murphy faces two counts of attempted murder and one count of aggravated assault. He was being held without bail in the Hernando County Detention Center.

The Sheriff's Office gave this account:

Murphy, who worked weekend nights and was not on duty, parked his car a few hundred yards from the building at 7030 Evergreen Woods Trail and sneaked in about 12:30 a.m.

He entered Lepp's room and threatened to harm her if she didn't stay quiet. He then walked down the hall to Giambrone's room and beat him in the face with the jack.

Lepp pressed her call button and summoned a nurse, who arrived to find Murphy beating Lepp with the jack. The nurse called security guard Jonathan Sousa.

When Sousa arrived, Murphy took a swing at him. Sousa grabbed and held Murphy until deputies arrived.

"I think what he did was nothing less than heroic," Nienhuis said of Sousa, who is also in his 20s.

Asked about a motive, Nienhuis said investigators believe that Murphy was living in his car, was addicted to or under the influence of drugs, and might have been looking for food.

"But as far as the attacks themselves, it's beyond comprehension," he said.

In a statement, Atria officials said Murphy passed the required background check and drug screening before he was hired about four months ago. The company expressed sympathy to the victims and their families and is offering counseling to residents and staff.

State records show Murphy does not have a criminal history in Florida.

A sheriff's deputy knocked on the door of John and Elaine Sammon's Spring Hill home about 2 a.m. Thursday and said Murphy — Elaine's son and John's stepson — was in custody. The deputy wouldn't say for what, but wanted to make sure the Sammons and their other children were okay.

The couple didn't find out about the horrific accusations against Murphy until later, when John Sammon showed up to his job as a maintenance worker at Atria. He'd helped Murphy get his job there.

The Sammons said the accusations left them stunned.

"It's a nightmare," Elaine Sammon said, her voice breaking and her eyes welling with tears. "It's not something I thought my son would have ever done."

His eyes red from crying, John Sammon said he knows all the residents at the facility, including Lepp and Giambrone.

Could they have angered Murphy in some way?

"I can't picture that," Sammon said. "They're too sweet."

Elaine Sammon said her son moved out a month ago after she suggested it was time for him to live on his own. He wasn't cleaning up after himself and was coming and going as he pleased, but didn't show any signs of volatility, she said. The couple said he has no history of mental illness.

The Sammons offered apologies and prayers to Lepp and Giambrone.

"I gave my kids the best upbringing I could," Elaine said. "We're Catholic, we went to church ... ."

"Sometimes," John Sammon said, "it's still not enough."

News researcher John Martin contributed to this report. Reach Tony Marrero at tmarrero@tampabay.com or (352) 848-1431. Follow @tmarrerotimes on Twitter.