A Ukiah man who was drummed out of the city’s police force in the 1990s after stealing money from a prisoner pleaded guilty Friday to repeatedly molesting a young girl, prosecutors said.

In an unusually rapid conclusion to the case, David John Richard, 52, pleaded guilty to a felony charge of continuous sexual abuse of a child under 14, the Mendocino County District Attorney’s Office said Friday.

Richard was arrested one week ago on suspicion of sexually abusing a girl for several months when she was 7 to 8 years old, the Mendocino County Sheriff’s Office said.

The girl, now 11, disclosed the abuse to the county Department of Child Protective Services in mid August, triggering an immediate investigation.

Richard committed at least five and up to 10 or more acts of “substantial sexual conduct” over an 18-month period, prosecutors said.

Richard accepted a stipulated state prison sentence of 16 years, with any credits he might earn limited to 15 percent of that term. He will be required to register as a sex offender for the rest of his life after he is released.

The fast-moving plea deal was handled directly by District Attorney David Eyster and Deputy District Attorney Beth Norman. Superior Court Judge John Behnke, who accepted the plea Friday, will formally sentence Richard on Oct. 13. He was held without bail at the Mendocino County Jail.

Richard, who served as a police officer in Ukiah for 2½ years, embarrassed the Ukiah Police Department in 1991 when he stole $200 from an undercover state agent posing as a drunk migrant worker.

Previously, two men arrested by Richard for being drunk had claimed he stole about $100 after taking them into custody. The report triggered a two-month investigation, ending with the decoy operation outside a Ukiah bar.

Richard, who was dispatched to arrest the undercover agent, took money from the agent’s wallet on the way to jail, according to court testimony. He pleaded guilty to grand theft and was discharged from the police force.

“It’s the most appalling thing I’ve ever seen,” Police Chief Fred Keplinger said in 1991.

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.