CHICAGO (CBS) — Chicago Public Schools Inspector General Nicholas Schuler resigned on Monday.

His resignation comes on the heels of a months-long investigation into complaints that Schuler created a “toxic work environment,” threatening and insulting workers in the office.

As CBS 2 Investigator Megan Hickey reported Monday evening, Mayor Lori Lightfoot accepted Schuler’s resignation Monday morning. It is effective Feb. 29.

In a statement, Mayor Lori Lightfoot said she accepted the resignation of the school district’s watchdog.

“The mayor thanks Mr. Schuler for his years of dedicated service to Chicago Public Schools and the City of Chicago. The Chicago Public Schools inspector general performs the critical role of ensuring the integrity of important functions within Chicago Public Schools, particularly regarding allegations of sexual assault or abuse. As a result, the mayor’s office will immediately begin the search for a replacement to ensure the rights of all students, teachers and staff remain protected.”

Meanwhile, a source close to the CPS Inspector General’s office confirmed that an investigation has been going on for at least six months into the toxic work environment created by Schuler, including regular physical threats and personal insults.

An outside law firm is conducting the investigation, a source close to the CPS IG office told CBS 2.

CPS declined to comment on Monday.

Schuler responded in an email to Hickey saying he had no comment other than, “I’m proud of the work we have accomplished here over the past five years.”

Schuler’s tenure as the CPS watchdog included investigations that led to the removal of two Chicago Public Schools chief executive officers.

First, Barbara Byrd-Bennett was probed for her involvement in a kickback scheme and resigned in 2015.

Byrd-Bennett was indicted for steering more than $23 million in no-bid contracts from CPS to her former employer, SUPES Academy, in exchange for $2.3 million in kickbacks. However, Byrd-Bennett never pocketed any proceeds from the scheme.

She ended up pleading guilty to one count of mail fraud, and in April 2017, she was sentenced to 4 1/2 years in prison.

And then in December 2017, CPS Chief Executive Officer Forrest Claypool ended up resigning for lying to cover for a friend.

Schuler alleged that the system’s top attorney, Ronald Marmer, violated the CPS ethics code, and that his close friend, Claypool, tried to cover up the violation.

Marmer, a former lawyer at Jenner & Block LLP, supervised a $250,000 CPS contract with the international law firm. At the same time, he was still receiving severance pay from them.

“Any other lying employee with this much evidence against them regarding lies and in different interviews would be fired,” Schuler said of Claypool in December 2017. “There would be no question about it.”

Schuler led an office of almost 50 employees.

His investigations uncovered employees falsifying work hours, disclosure of confidential student information, and irregularities in the Pre-K program – among dozens of other topics.

Most recently, an IG investigation into last school year found more than 30 instances of sexual misconduct and other disturbing behavior by teachers and others who work in the schools.

On Monday, the Mayor’s office did not comment on the investigation into Schuler’s own alleged misconduct.

Schuler was appointed by former Mayor Rahm Emanuel in 2014. It’s up to Mayor Lightfoot to now choose his replacement.

On Monday, the Mayor’s office said that search will begin immediately.

Megan Hickey