LOS ANGELES -- A former teacher who pleaded no contest to sex-related charges involving four special education students was sentenced Wednesday to three years in state prison.

Los Angeles Superior Court Commissioner Henry J. Hall denied probation for 60-year-old Fred David Johnson, noting that the crimes involved a "breach" of trust involving "particularly vulnerable" victims entrusted to his care.

"I don't think probation is an appropriate sentence," the commissioner said.

He noted that the former John Marshall High School special education teacher had no prior record and admitted his culpability at an early stage in the criminal proceedings.

In a letter read by his family's attorney, one of the victims said he wanted Johnson to serve 20 years or more behind bars for his crimes, which went on for about eight months last year.

Three of the victims' mothers also gave tearful statements, with two of them saying through a Spanish interpreter that they wanted justice.

Johnson pleaded no contest Jan. 30 to one felony count of oral copulation of an incompetent person involving a 14-year-old boy. He also pleaded no contest to two misdemeanor counts of child abuse involving a 17-year-old boy and a 17-year-old girl and one misdemeanor count of battery on a mentally disabled 19-year-old man.

Johnson has been jailed since his arrest last Aug. 20.