by Todd Feurer, CBS Chicago web producer

CHICAGO (CBS) — Though questions continue to swirl about the night he was found slumped behind the wheel of his car, after he’d been drinking at dinner with friends, Police Supt. Eddie Johnson insisted Thursday the ongoing investigation was not a factor in his decision to retire at the end of the year.

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Rather, Johnson said the only reason he’s calling an end to his 31-year career with the department is the toll the job has taken on him and his family.

“It’s taken a toll on my health, my family, and my friends, but my integrity remains intact, and I’m proud of what the department has accomplished in my tenure,” he added.

Johnson has had a series of health issues since taking the top post at CPD, including high blood pressure and kidney disease, which required him to receive a kidney transplant from his son in 2017.

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As for any cloud that might be left hanging over his head when he steps down, given the investigation into being found asleep behind the wheel of his car, Johnson said people can speculate all they want.

“My glass is always three-fourths full, and today is no different. I choose to focus on the positive things,” he said. “I’ve been doing this 31 years. It’s time. 2020 will be a new year, and a new chapter in my life, and I’m looking forward to it. I’m so at peace, mentally, with everything.”

Johnson was found asleep behind the wheel of his SUV early on Oct. 17, after he had gone out for dinner with a group of friends the night before. Speaking before a Police Board meeting the evening after the incident, Johnson blamed the incident on a mix-up in which he failed to take his blood pressure medication, and a feeling that he might faint that prompted him to pull over and rest.

Lightfoot later told said Johnson had admitted to her in a phone call that he’d had “a couple of drinks with dinner” that night. Chicago Inspector General Joseph Ferguson is now investigating the incident.

Johnson and Mayor Lori Lightfoot have refused to discuss the investigation, citing the need for the probe to remain independent.

“The investigation, I’m sure, because it’s the inspector general, will be very thorough, but it’s inappropriate for us to talk about anything related to the investigation, because [Johnson is] going to be a witness, I’m going to be a witness,” Lightfoot said.

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Johnson said he began talking to the mayor about possibly retiring in September — before the incident in his car — when he attended a memorial ceremony at Gold Star Families Memorial for three police officers who were killed in the line of duty last year. The superintendent choked up as he recalled speaking to the fallen officer’s widows.

“Not only could I see pride in their faces, but I also saw the pain in their faces, and I also saw the reflections of their husbands,” he said. “The mayor and I were sitting next to the waterfall, and when I sat down in that seat, I leaned over to her and whispered in her ear, ‘We’ve got to start talking about an end date for me,’ because that … losing those officers was hard.”

A month after that, Johnson went to London with his family to watch the Chicago Bears play the Oakland Raiders, which was his first vacation since becoming superintendent. He said that trip essentially convinced him it was time to retire.

“Since I’ve been superintendent, we hadn’t had the chance to spend that kind of time together,” he said. “It made me feel normal, and I saw them, how they missed me in that kind of setting, and that’s pretty much what did it. I just can’t keep punishing them.”

Johnson said he never dreamed of being in the position of the city’s top cop in the first place, until Mayor Rahm Emanuel hand-picked him for the job in 2016.

“Rahm Emanuel saw something in me that I didn’t see in myself, and I have led the nation’s second-largest police department ever since,” Johnson said.

Johnson said his story began as it has for far too many children who have grown up in Chicago, as a witness to the devastating effects of gun violence.

“I saw how these unspeakable acts could tear a family apart. I also saw how those were sworn to protect our city instead relied on prejudice and intimidation. So I could have easily learned to hate this city, but my family taught us to love it,” Johnson said.

The superintendent said, as a child, his parents “set an example that continues to serve as the foundation for who I am today.”

“They worked hard. They taught us to always do our best. They taught us to always do what’s right,” he said.

From a kid growing up in the Cabrini-Green public housing development to Chicago’s top cop, Johnson said he hopes his story inspires the next generation of police officers.

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“The best leaders don’t bark orders or point fingers. They lead by example, and I hope that the example that I’ve set inspires someone. Maybe another kid from the South Side. Maybe it inspires that kid to work hard, and do the right thing, and maybe even join the department,” he said.