After seven days of deliberations, a jury found John Phillip Moncrief guilty Monday of first-degree murder in the beating death of the 6-year-old daughter of his former girlfriend.
Moncrief, 31, faces a maximum sentence of 25-years-to-life in state prison.
San Diego Superior Court Judge Terry O'Rourke set sentencing for Feb. 22.
The jury acquitted Moncrief of threatening his former girlfriend, Linda Williams, 34, or her 13-year-old son, Matthew Moss, from testifying in the case.
The victim, Amber Avey, had more than 30 fractures of her ribs and pelvis. A prosecutor said the injuries were suffered during a vicious beating Feb. 21, 1986.
Moncrief's attorney, C. Logan McKechnie, argued that the girl died after accidentally falling out of a van her mother was driving and was run over. He said her injuries could not have been caused by a human.
Her body was found in a shallow grave Sept. 22, 1986, near the San Diego River in Mission Valley after Williams told police where to find it.
Jury foreman Anthony Bowker said the jury threw out the accident story after deliberating for several days. "We first had to determine if it was an accident," he said. "None of us could understand . . . how a mother could sit there and let it happen."
McKechnie said he will appeal the verdict. The trial began in early December, and deliberations began Jan. 14.