By Alex Dobuzinskis

LOS ANGELES (Reuters) - A former Los Angeles County Sheriff Department's captain charged in a probe of jail abuse pleaded guilty on Wednesday to lying on the witness stand, officials said.

Under his plea agreement, William Thomas Carey, 57, must cooperate with U.S. prosecutors in the case against a retired second-in-command at the department.

Carey entered his guilty plea in federal court in Los Angeles and faces up to five years in prison when he is sentenced on Jan. 25, said Thom Mrozek, a spokesman for the U.S. Attorney's Office.

Carey had run a bureau that investigated cases of suspected abuse of inmates by deputies at the Sheriff's Department, which runs the nation's largest jail system.

In May, a grand jury indicted Carey and former Undersheriff Paul Tanaka in a case stemming from a long-running federal investigation of corruption and suspected abuse of inmates at two downtown Los Angeles jails.

As part of his agreement with prosecutors, Carey pleaded guilty to lying on the stand during the trial last year of a sheriff's deputy later found guilty of trying to obstruct the investigation.

The deputy was one of seven sheriff's officers convicted for their roles in blocking the probe.

In exchange for his guilty plea and for his cooperation, prosecutors have dropped charges of conspiracy and obstruction of justice against Carey, according to the plea agreement.

He is required to appear as a witness at trial if called.

Tanaka, meanwhile, is scheduled to go on trial on Nov. 3. He is charged with conspiracy and obstruction of justice.

Federal prosecutors have said that Tanaka and Carey arranged in 2011 to have two sergeants approach an FBI agent outside her house when she was investigating the jails, threaten her with arrest and attempt to intimidate her.

Sheriff's officials also hid an FBI informant at a jail, preventing him from contacting his handlers, prosecutors said.

An attorney for Tanaka, H. Dean Steward, could not be reached for comment.

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Last week, after it was revealed Carey reached an agreement with prosecutors, Steward told the Los Angeles Times he did not expect Carey would be called to testify against his client.

"Once you've admitted to lying on the stand, who can believe anything you say?" Steward told the paper.

Tanaka, until he retired in 2013, served as second-in-command to Lee Baca, the Los Angeles County sheriff at the time.





(Reporting by Alex Dobuzinskis; Editing by Daniel Wallis and Eric Walsh)