MOORPARK - Authorities called off a search today for the remains of a boy killed 40 years ago by a prolific San Fernando Valley serial killer.

The bones of 16-year-old Roger Dale Madison will probably remain beneath the 23 Freeway, said Los Angeles police Detective Vivian Flores, who was in charge of the investigation.

Madison was killed by Mack Ray Edwards, a Pacoima man who confessed to befriending, then molesting and killing at least six children in the 1950s and '60s. He hung himself on death row in 1971.

Forensics experts dug a 20-foot-deep pit at the side of the freeway, where search dogs and scientific techniques indicated a human body had been buried. Flores said the dogs and equipment could have been detecting chemicals that "leeched" into the soil surrounding the body as it decomposed.

But, she added that the remains are likely underneath the freeway itself, and crews would have to shut down the 23 to continue digging.

Madison's sister, Sharon Barlow, visited with the crews today and placed a bouquet of red roses at the edge of the open pit. She hugged the digging crews and shed a few tears.

"I know he's there and I understand why they can't dig any further," she said, adding she would consider the site, alongside the southbound offramp at Tierra Rejada Road, a makeshift grave for her brother.