Stanton, Calif. ? A factory worker acquitted of molesting two girls two years ago was arrested Friday in the kidnapping and slaying of 5-year-old Samantha Runnion, whose abduction sent a chill across Southern California.

Orange County Sheriff Michael Carona said a tip from the public led authorities to the 27-year-old suspect, Alejandro Avila.

“I am 100 percent certain that Mr. Avila is the man who kidnapped and murdered Samantha Runnion,” Carona said during a news conference Friday about eight hours after announcing the arrest.

Avila was detained at his mother’s apartment in Lake Elsinore, about 50 miles from Stanton and about 10 miles from where the body was found.

No charges were announced against Avila, but Carona said the case was “ready to be handed over to the District Attorney’s Office.”

Before his arrest, Avila denied any involvement in the slaying during an interview with the Los Angeles Times and said he told detectives that he was at a mall when Samantha was kidnapped.

He said detectives told him they had found fibers on the body they considered key evidence.

The sheriff credited the speedy arrest to solid forensic and scientific investigation as well as tips from the public and the media’s work in spreading news of the abduction and the suspect’s description.

Carona became emotional when he described the extent of his investigators’ efforts to solve the crime.

“This is a message from me on behalf of Samantha’s family to Mr. Alejandro Avila: What you didn’t realize when we found Samantha’s body and this investigation took place, Samantha became our little girl,” he said.

The girl’s mother, Erin Runnion, 27, remained in seclusion Friday. Assistant Sheriff George Jaramillo said she was grieving and “arresting the right guy or anybody doesn’t change that reality.”

Samantha was playing with a friend 50 yards from her front door Monday evening when she was dragged kicking and screaming into the light green car of a man who had asked for help in finding his puppy.

A 5-year-old playmate witnessed the kidnapping and investigators launched an intense manhunt using her description of the man and the car he drove.

An acquaintance said Avila was familiar with Samantha’s apartment complex because he used to visit someone there a few years ago, before the Runnions moved in.

Avila’s mother, Adelina Avila, said her apartment was searched by authorities late Thursday.

“I don’t think my son did anything, but I notice he is cooperating,” she said. “He hasn’t been through this before so he doesn’t know what’s going on. He doesn’t have a record.”

Two years ago, Avila was charged with molesting two girls under 14 but was acquitted by a jury, Riverside County Deputy Dist. Atty. Paul Dickerson said. He said he did not have details of the case.

Samantha’s nude body was discovered Tuesday on the edge of a forest, along a highway that connects Lake Elsinore with the suburban communities of Orange County, including Stanton. Authorities said she had been sexually assaulted and suffocated.

Avila has worked since September as an assembler at the Temecula plant of Guidant Corp., which makes pacemakers and similar medical devices. A spokesman said the company was cooperating with investigators.