The investigation, conducted by Sen. Chuck Grassley's office, concluded it was "more probable than not'' that the aide, Rick Jacobs, "sexually harassed multiple individuals and made racist comments towards others."
"Based on witness testimony, this behavior was pervasive, widespread and notorious,'' according to the report. "Several individuals told investigators that Mayor Garcetti was aware of this behavior, and based on the reported frequency and conspicuous nature of the conduct, it is more likely than not that Mayor Garcetti either had personal knowledge of the sexual harassment or should have been aware of it.''
RELATED: Former Garcetti communications director says mayor should be charged with perjury, files complaint
Later Tuesday, Garcetti issued a brief statement in response to the report: "While I strongly disagree with the opinion reached in this report, I am pleased that Senator Grassley has lifted his hold, and hope that my nomination by the President can be considered by the Senate soon."
ABC7 has reached out to the White House for comment.
Investigators interviewed 15 witnesses, read 26 depositions taken in a lawsuit and consulted other materials, including emails and text messages. The report said Garcetti and Jacobs declined to be interviewed.
Garcetti's nomination by President Joe Biden to become U.S. ambassador to India has languished since July and it's not known when a vote will take place, if at all. If Garcetti remains at City Hall, his term runs through the end of the year.
In March, Grassley, the top Republican on the Senate Judiciary Committee, said in a statement he has received "numerous credible allegations" that Garcetti was aware of sexual harassment of city employees committed by his former adviser and close friend Rick Jacobs, but did nothing to stop the misconduct.
Garcetti has denied witnessing or being told of any inappropriate behavior by Jacobs. A lawsuit against the city charges that Jacobs frequently sexually harassed one of the mayor's police bodyguards while Garcetti ignored it or laughed it off. Jacobs has called the allegations against him "pure fiction."
Garcetti testified under oath, telling senators that if he witnessed the harassment, he would have done something about it.
"It's not good for Mayor Garcetti because it makes it look like he lied under oath to the senators," Loyola Law School professor Jessica Levinson told ABC7. "It makes it looks like he couldn't run an office without sexual harassment and racist comments, and that's not the person you want as the ambassador."
Grassley's report has new witnesses and allegations that state Garcetti knew about the harassment.
The report also criticizes an investigation conducted by the city attorney's office that didn't interview Jacobs the first time and cleared the mayor.
Biden has stuck by Garcetti throughout Grassley's investigation, even amid a report that Senate Majority leader Chuck Schumer didn't have the votes to confirm Garcetti.
"It's easy to envision a situation where Mayor Garcetti loses at least one Democrat senator and that's fatal in an evenly divided Senate like this," Levinson said.
The Associated Press contributed to this report.