LOS ANGELES (CBSLA.com) — Former Los Angeles County Sheriff Lee Baca plead not guilty Friday to federal charges of conspiring to obstruct justice, obstructing justice and lying to the federal government.

Baca’s arraignment in Los Angeles federal court comes a week after being indicted for allegedly trying to undermine a covert FBI investigation into corruption and brutality by jail deputies.

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The 74-year-old ex-sheriff previously backed out of a plea deal on the lying count, which had been reached with federal prosecutors earlier this year. A federal judge had balked at the plea agreement, which called for Baca to serve no more than six months behind bars and said it was too lenient considering the retired lawman’s role in obstructing an FBI investigation into Los Angeles County jails.

Rather than face a penalty of up to five years in prison, Baca withdrew his guilty plea – opening him up to the more wide-ranging indictment.

If convicted of all charges, Baca, who is suffering from the early stages of Alzheimer’s disease, could face up to 20 years in federal prison, according to the U.S. Attorney’s Office.

A judge has set a tentative trial date of Oct. 4.

Baca, who ran the nation’s largest sheriff’s department for 16 years, is accused of participating in a wide-ranging conspiracy to derail the FBI’s probe of corruption and brutality within the walls of Men’s Central Jail.

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After jail guards discovered that an inmate, Anthony Brown, was an FBI informant, they booked him under false names and moved him to different locations in order to keep him hidden from federal investigators. They also went to the home of an FBI agent and threatened her with arrest.

Ten former sheriff’s department officials, including Baca’s former top deputy, Paul Tanaka, have been convicted or pleaded guilty in connection with the obstruction case.

Tanaka, who claimed his former boss ordered the department’s response to the federal jails probe, was sentenced to five years in prison but is free pending appeal.

Baca had served as sheriff since December 1998, before retiring in 2014, at the height of the federal probe.

A federal appellate panel recently upheld the convictions of seven former sheriff’s department officials convicted in the conspiracy.

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