A recent news investigation reveals how a serial pedophile managed to remain employed in public schools for more than a decade despite numerous red flags, ultimately abusing hundreds of children.

Chicago Public Schools fired teacher Thomas Hacker in 1980 when a student complained to school officials that Hacker was sexually abusing his classmates. Nine years later he was convicted of the aggravated sexual assault of an 11-year-old Boy Scout and sentenced to 100 years in the Big Muddy River Correctional Center, where he died in June, the Associated Press reports.

The Chicago Tribune has since combed through Hacker’s testimony in depositions, public records and personnel files “obtained through a source,” and other records to sketch out how a man alleged to have molested hundreds of young boys in Illinois and Indiana over two decades managed to remain employed in schools.

“Hacker’s trail of serial abuse began at a time before today’s interstate criminal background checks, before web-published sex offender registries and before cultural awareness encouraged sex abuse victims to speak out – factors that helped him elude scrutiny,” the Tribune reports.

Hacker was initially hired by Chicago Public Schools in 1970 just three months after he was convicted of molesting a 14-year-old Indiana boy, though there’s no indication Chicago officials were aware. He worked at two South Side elementary schools and mentored suburban boys through the Boy Scouts and church groups. Less than a year after he was hired at CPS, Hacker was convicted of sexually abusing a child in Mount Prospect, then again Oak Lawn five years later, the Tribune reports.

Despite the convictions and accusations from students at school, Hacker was simply transferred and avoided serious consequences. After one accusation from a CPS student, Hacker recalled, an administrator told the teacher “he’ll give me the benefit of the doubt but he would watch me pretty carefully,” according to a deposition.

It didn’t work, and Hacker simply came into class early and found other ways to take advantage of students.

He also continued to abuse boys through the Boy Scouts and church groups.

The Tribune reports:

Hacker’s Boy Scouts and church victims said in court statements that they saw or experienced his anal rapes as well as humiliating rituals involving oral sex and group masturbation. Hacker testified from Big Muddy that he usually lost sexual interest in boys after they reached puberty but inculcated former victims to assist in his abuse of boys ages 10 and 11.

He ingratiated himself to the parents of boys he abused, prayed with his child victims and then threatened them to keep his secrets, according to Hacker’s two court depositions and the police statements of his young victims.

CPS officials apparently were not aware or did not take action to fire Hacker despite convictions in 1970, 1971, and 1976, none of which resulted in jail time.

He continued to teach until 1980, when a student reported his behavior to a principal at Haines Elementary School who finally took action.

“He just dropped a note in the principal’s office saying I was exposing or, you know, pulling down the pants of some of his friends before and after school,” Hacker said in a deposition. “That basically ended my teaching in the Chicago Public Schools.”

But it didn’t end Hacker’s reign of terror.

He continued to sexually abuse young boys for another nine years – racking up at least 34 more victims – before he was eventually sentenced to prison for the rest of his life, the Tribune reports.

His alleged victims are now pursuing lawsuits against CPS and other entities that Hacker worked for, though CPS initially denied the teacher ever worked in the school system.

“There’s a lack of any acceptance of responsibility by CPS,” attorney Christopher Hurley, who represents six of Hacker’s victims, told the Tribune. “Their policy has always been secrecy, secrecy, secrecy.”