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Alex Villanueva was officially sworn in as the new Los Angeles County Sheriff on Monday, after defeating incumbent Jim McDonnell in a rare runoff election.

Villanueva, a retired sheriff’s lieutenant with no experience at the upper levels of law enforcement, managed to succeed by appealing to a heavily Democratic constituency, promising reforms like removing immigration agents out of the county’s jails.

In the packed auditorium at the East Los Angeles College, Villanueva thanked his supporters after taking the oath of office.

“This was a rare moment in history where we not only had the opportunity but courage and responsibility to challenge an existing power, to ensure that no matter where you’re from, where you live, how you pray, the color of your skin, your sheriff’s department will work to protect you and keep you safe,” Villanueva said at his swearing-in ceremony.

Villanueva took the stage with his wife, a more than 30-year veteran of the L.A. County Sheriff’s Department, and thanked her for bearing “the brunt of retaliation leveled my way for years and she did so with dignity and grace.”

“Viv, I love you. I couldn’t have only done this without you by my side,” Villanueva said before kissing and embracing his wife while the crowd clapped and cheered.

At the ceremony, Villanueva also spoke in Spanish, addressing recent Spanish-speaking immigrants, “I am here to serve you” he said.

The new sheriff is the first candidate to unseat a living L.A. County sheriff in over 100 years, according to a news release by the Sheriff’s Department. He is the county’s 33rd sheriff.

Incumbent McDonnell, who was seeking his second term as sheriff, was initially leading in the elections, but Villanueva took the lead when additional mail-in and provisional ballots were counted. He proclaimed victory on Nov. 16.

McDonnell did not concede until last Tuesday.

Once in office, Villanueva will have to deal with the growing concerns about the future of reforms imposed by former Sheriff McDonnell, dealing with a culture of violence in the jails and serious wrongdoings by top department officials.

“What was behind us pales in comparison to the challenge in reform that lies ahead of us,” Villanueva said. “If I say we can reform his department, you should believe me. We can.”

The new sheriff pinned two assistant sheriffs at the swearing-in ceremony: industry station Capt. Tim Murakami and commander Maria Gutierrez. Retired Cmdr. Ray Leyva will be the new undersheriff.

“It is a privilege to serve you and I only ask that you serve your community with dignity and pride. Treat everyone with respect,” Villanueva said to LASD officers at the ceremony. “The success of your career will be determined by how well you serve the community, not the political powers that be. Those days are over.”

Villanueva is expected to remove several top officials from office, including four assistant sheriffs, eight chiefs, a communications director and a community outreach director, the Los Angeles Times reported.