CHICAGO (CBS) — In the mid 1970s, detective Ron Stallworth, a black man, joined the Ku Klux Klan.

The twisted tale is now a movie currently in theaters. But on Sunday at St. Sabina’s church, the real Stallworth told his story from the pulpit.

CBS 2’s Jeremy Ross has more on why the former Klansman calls Chicago home and isn’t afraid to speak out against the Klan.

There are things you expect to see and hear in church. This is not one of them.

“I said ‘I hate blacks, Mexicans, Asians and anyone else who isn’t pure Aryan white like I am,'”

Retired police officer Ron Stallworth spoke to St. Sabina congregants about the letter he wrote that helped him infiltrate the ranks of the KKK while he was Colorado Springs’ first African American detective.

“We conned the KKK,” said Stallworth.

His 1978 story retold in the movie “BlacKKKlansman” where he responds to a newspaper personal ad looking for KKK members, receives a call of interest, then working with a white officer who takes on his identity, gathers info on the Klan during face-to-face meetings.

Two different men with two different voices.

“As I wrote in my book, they were not the brightest lights in the socket,” said Stallworth.

(Credit: CBS)

While signing his New York Times best-selling book, Stallworth calls Chicago home, spending the first four years of his life on the South Side.

Stallworth added he wasn’t shocked to learn about KKK recruitment flyers spotted in Tinley Park this past summer.

“Handing out pamphlets is a common tactic of the Klan and other white supremacy groups,” Stallworth said.

The former detective admits no arrests were made in connection with his Klan investigation. He said that was not the intent of his work. But kept members from burning at least two crosses.

And kept a keepsake.

A KKK membership card, signed by former Grand Wizard David Duke. Proof that he was a card-carrying member of the Klan who may have acted, but never looked the part.

“Dr. King said we will overcome. And I want you to know that after dealing with these fools sooner rather than later, we will overcome.”

(Credit: CBS)

During an interview, Duke called the premise of the movie ‘a lie.’ Stallworth, however, said Duke called him later to tell him he liked his book and respected him.