by Todd Feurer, CBS Chicago web producer; CBS 2’s Suzanne Le Mignot and Dana Kozlov contributed to this report

CHICAGO (CBS) — As Interim Supt. Charlie Beck takes the reins of the second largest police force in the country, the department is facing some significant turnover in its top ranks in the wake of former Supt. Eddie Johnson being fired.

Sources told CBS 2’s Suzanne Le Mignot about 20 high-ranking officers are planning to retire. Most of those officers were appointed to their current positions by Johnson, whom Mayor Lori Lightfoot fired on Monday.

However, CPD spokesman Anthony Guglielmi could only confirm Deputy Chief Dwayne Betts, Deputy Chief of Patrol George Devereux, Chief of Organized Crime Salvador Avila, and Commander of Airport Law Enforcement Thomas O’Brien have actually submitted retirement paperwork.

Sources said among those expected to hand in retirement papers include captains, commanders, lieutenants, and deputy chiefs.

Guglielmi also said Beck demoted Grand Central District Cmdr. Anthony Escamilla on Tuesday because he wanted to go in a different direction for leadership in the district.

“Commanders are appointed positions, so (Escamilla) will return to his rank of Captain,” Guglielmi wrote.

Beck, during his first press conference as the city’s top cop on Tuesday, said the changes in the top ranks are “natural.”

“A number of people are retiring in very important positions. They will have to be replaced. Obviously, the selection of a new superintendent will be a huge change,” he said.

RELATED: Day After Firing, Eddie Johnson Denies He Misled Mayor Ligthtfoot, But Admits ‘Lapse of Judgment’

Beck, former chief of the Los Angeles Police Department, had a meeting with police officers at Area Central headquarters on Monday after Johnson was fired. Sources said he told officers there would be some “big changes” at the department, but he did not elaborate what they were going to be.

For his part, Beck said he spent most of the day on Monday assuring officers in the department that there would be a smooth transition as he takes command.

“I believe that they have done incredible work over the last three years, that their work is important to me, that I believe in them as a police agency,” Beck said. “I have some things I can bring to the table from a different perspective, having policed another city for a very very long time, but that is not to take away from the success that this department has had.”

Beck is serving as interim superintendent until the Chicago Police Board can complete a nationwide search for a new superintendent, and Mayor Lightfoot can appoint one of the finalists selected by the board.

RELATED: Eddie Johnson’s Time As Police Superintendent Started With Ambition, Ended With Controversies

The change in leadership at CPD came about four weeks earlier than expected, after Lightfoot fired Johnson on Monday. Johnson had been set to retire at the end of the year, but Lightfoot terminated him for cause for lying about the night he was found slumped behind the wheel of his car in October.

“This is not at all how I envisioned the transition, but – and I think this is very important – this will not deter the transition,” Beck said.

While Johnson is no longer with the department, Beck said he will stay in contact with his predecessor as he takes over at CPD.

Beck declined to comment on the circumstances of Johnson’s firing, but said they remain friends.

“None of us are perfect. Everybody makes mistakes, but we have to live with that, and we have to live with our errors,” Beck said.

Lightfoot was visibly furious as she announced that she was firing Johnson, accusing him of intentionally misleading her and the public.

“A lie is a lie,” Lightfoot said at a Monday morning news conference. “He told me something that happened that night that turned out to be fundamentally different than what he portrayed to me and what he portrayed to members of the public.”

The mayor said a city Inspector General’s report and video evidence from the investigation make it clear Johnson lied about the circumstances of the incident.

Lightfoot declined to go into specifics about what Johnson lied about, “out of deference to his wife and children,” but sources told CBS 2 Johnson had been out drinking with a woman who was not his wife hours before he was found asleep at the wheel.

Sources said the woman with whom Johnson had been drinking that night at Ceres Café, in the Board of Trade Building at 141 W. Jackson Blvd., is also a Chicago Police officer.

Lightfoot said Johnson intentionally misled her when they personally discussed the incident, and also lied to the public when he held a press conference several hours after it happened.

“He was not caught off-guard, and he had plenty of time to choose his words, and the choice he made was to communicate a narrative replete with false statements, all seemingly intended to hide the true nature of his conduct from the evening before,” she said.

During that press conference following the Oct. 17 incident, Johnson blamed the incident on a mix-up with his medication, but did not mention that he had been drinking before he fell asleep behind the wheel of his car. The mayor later revealed that Johnson had been drinking that night, but kept him in the job while Inspector General Joseph Ferguson’s office investigated the incident.

On Monday, Lightfoot said her review of the inspector general’s report on the incident, as well as video evidence, convinced her Johnson had lied about the incident, calling his actions “intolerable.”

The mayor declined to discuss the specifics of the inspector general’s investigation until the report is made public. Lightfoot said the inspector general is still investigating the actions of others involved in the incident.