A former custodian a Central Coast California elementary school was convicted of producing and possessing child pornography after investigators found more than 120,000 images on his computer including nearly three dozen pictures of a 4-year-old granddaughter of a friend, officials said.

Shane Robert Ferguson, 34, of Atascadero, Calif., was found guilty late Thursday by a federal jury. Ferguson was convicted following a trial lasting more than two days at the United States District Court in Los Angeles.

The investigation into Ferguson began in July 2005, when the grandparents of the 4-year-old victim reported suspicions of child molestation to the Atascadero Police Department. A search of Ferguson’s apartment by investigators recovered a computer, computer media and videotapes, according to the United States Attorney's Office in Los Angeles.

A computer forensic examination by the San Luis Obispo Sheriff’s Department showed the computer held more than 120,000 images of child pornography, including images of the 4-year old victim. Officials said that during this week’s trial, the jury saw a videotape where Ferguson confessed to taking pictures of the girl.

Ferguson, scheduled for sentencing by United States District Judge J. Spencer Letts on July 13, faces a minimum sentence of 15 years in federal prison, and a maximum of 40 years.

Ferguson worked at Santa Margarita Elementary School in Atascadero.