Warning Shot Inadvertently Kills Boy, 14 : Inquiry: Rancher is arrested. Authorities say he was trying to send a signal to teen-agers tampering with his car.

A wheelchair-bound Acton man who fired a warning shot when he saw two teen-agers tampering with his car Thursday night inadvertently killed a third youth he did not see, authorities said.

In a heart-breaking twist, friends say the rancher, Malcom McWilliams, 52, only wanted to get the boys’ attention so that he could tell them about a recent joy-riding accident that killed one of his granddaughters and gravely injured another.

“He thought he was doing a good deed,” said Cindy Giles, who lives in a trailer on the ranch. “He never saw the third kid.”

When he was arrested early Friday, McWilliams was “very cooperative and very upset about the shooting,” said Sheriff’s Deputy Benita Hinojos.

He was booked into a jail ward at County-USC Medical Center on suspicion of involuntary manslaughter. The district attorney’s office will decide whether criminal charges will be filed.

McWilliams remained in custody Friday in lieu of $15,000 bail.

Friends said McWilliams was the grandfather of JoKema Du Bois, 15, of Santa Clarita, who took her grandmother’s car without permission June 1 to attend a church youth group meeting. When the car crashed, JoKema and two of her passengers were killed. Two other girls were injured, including JoKema’s 14-year-old sister Barbara.

Malcom McWilliams is divorced from Mary McWilliams, who was raising the sisters, friends said.

In Thursday night’s incident, McWilliams is accused of fatally wounding Ernesto Luis Pedraza, 14, of Apple Valley.

Ernesto and two friends were staying at the Thousand Trails campground in Acton when they decided to hike down Bootlegger Canyon Road to steal McWilliams’ Chevette, Hinojos said.

At about 8 p.m., McWilliams heard someone tampering with his car, which was parked about 100 feet from his house. When he went outside, he saw two people trying to start the Chevette, deputies said.

From his patio, McWilliams fired one shot from a carbine rifle into an abandoned vehicle next to the Chevette.

“McWilliams did not fire into the air because he did not want anyone to be injured,” Hinojos said. “However, McWilliams did not know that a third boy was hiding behind the abandoned vehicle.”

The warning shot went through the abandoned vehicle and struck Ernesto, authorities said.

Unaware that Ernesto had been shot, McWilliams detained one of the boys at gunpoint and summoned sheriff’s deputies. The other youth fled.

When deputies took the youth who had been detained by McWilliams back to the campground, Ernesto’s guardians asked where he was, Hinojos said. The youth replied that his friend had been shot. Deputies found the boy’s body behind the abandoned car about two hours later, she said.

McWilliams’ neighbor, Giles, said McWilliams had been despondent in recent months over the accident involving his granddaughters. She said he fired the warning shot because he wanted to deliver a stern lecture.

“He wanted these boys to stand still, so he could tell them about JoKema and Barbara and how joy-riding was dangerous,” Giles said.

The neighbor, who went to McWilliams’ house after hearing the gunshot, said the rancher was unaware that his warning shot had killed Ernesto until the boy’s body was found at about 12:15 a.m. Friday. “The fact that he shot this kid just really upset him,” Giles said.

Bill Conrad, 70, of Watts, said he has leased the rugged 80-acre ranch to McWilliams for the last 25 years. Conrad said he believes McWilliams was paralyzed from the waist down from a bullet wound, but said the rancher doesn’t discuss his disability.

Over the years, McWilliams has raised horses and exotic animals such as ostriches at the ranch, Conrad said. At one point, he built an Old West movie set at the ranch but was unable to attract filmmakers, the owner said.

Inside his house, McWilliams has collected photographs of John Wayne and cowboy-related memorabilia. He also displayed awards received for his efforts as an auctioneer and square-dance caller.

More recently, McWilliams has developed medical problems that took him away from the ranch for long periods and left his property vulnerable to theft, Conrad said. The accident involving his granddaughters added to his woes.

“He became a basket case,” Conrad said. “I’ve been coming up once a week to talk to him and hold his hand.”

Phil Sneiderman is a Times staff writer and Mark Sabbatini is a special correspondent.