For 18 years, thousands of students at the University of North Carolina at Chapel Hill took classes with no assigned reading or problem sets, with no weekly meetings, and with no faculty member involved. These classes had just one requirement: a final paper that no one ever read.

The academic fraud in the university's African-American studies department was first revealed three years ago. But a new investigation shows that the fake classes were even more common than previously thought, and that athletes in particular benefited from the classes, in some cases at the behest of their academic counselors. Previous investigations had found no ties to campus athletics.

On campus, the fake classes, which at least 3,100 students took, were hardly a secret. They were particularly popular with athletes, who made up about half of enrollments. Nearly a quarter of students who took the classes were football and basketball players. And the classes made a difference: good grades that students didn't have to work for made more than 80 eligible to graduate who otherwise would have flunked out.

After the dubious courses were first revealed 2011, the university conducted two investigations. Today's was the third, and by far the most detailed, in part because investigators spoke to the two people at the heart of the scandal.

Here's what they found about how the scheme worked, why it was started in the first place, and why it worked for so long.

How the fake classes worked

Two members of the university's African-American studies department — Debby Crowder, the student services manager, and Julius Nyang'oro, the curriculum chair who later led the department — were responsible for the scheme, with Crowder leading it.

Criminal charges against Nyong'oro were dropped earlier this year; Crowder has never been charged. Both cooperated with the investigation, directed by former US Justice Official Kenneth Wainstein, a partner at the law firm Cadwalader, Wickersham & Taft.

According to Wainstein's report, Crowder created "paper classes." Some of these classes were independent studies, in which students are supposed to work one-on-one with a faculty member and write a final research paper. But there were no professors involved. (In the university's systems, Nyang'oro was listed as the person in charge of the classes, but he didn't actually work with students. Crowder signed his name to grade reports.) Crowder assigned and graded the final paper, the only requirement in the paper class. The grades were usually very high, even if portions of the paper were plagiarized or written at a middle-school level.

Then the "paper class" fraud spread beyond just independent studies, according to the investigation. Crowder began creating fake lecture classes. The classes never met, and operated just like the fake independent studies. Then Crowder enrolled students in actual lecture classes, but exempted them from all requirements except for a final paper. In some cases, she would add a student to a legitimate class. That student would fail or get an incomplete for never showing up or doing the work. After the student handed a paper in to Crowder at the end of the semester, she'd change the failure or incomplete to a high grade — without the knowledge or consent of the instructor.

Grades were about 10 percent higher than in other courses in the African-American Studies department: the average grade was 3.6, meaning virtually all students were getting an A or B on their sole assignment.

In some cases, the investigation notes, students took the research paper requirement seriously and put work into researching and writing about their assigned topics. But in many other cases, they turned in papers that were plagiarized, written by tutors, or that had only an introduction and conclusion with "fluff" in between. Crowder sometimes gave out passing grades even if students didn't turn in anything at all.

What the athletic department— and the rest of the university — knew about academic fraud

It's not unusual for colleges to steer athletes toward easier classes, or classes that fit their travel schedules while their sports are in season. And the investigation suggests that even if most people at the university didn't realize the paper classes were total frauds, some, including head basketball and football coaches, were aware that they were very, very easy.

Some counselors who worked in the university's Academic Support Program for Student Athletes knew the paper classes went far beyond being an easy A and were academic only in name. When Crowder announced her planned retirement, this side was shown to a group of football coaches:

At the rest of the university, though, people seemed aware the classes were easy — maybe too easy — but didn't know the extent of the fraud, according to the investigation. Within the African-American Studies department, some professors knew of Crowder's influence, particularly with student-athletes, and criticized Nyang'oro's leadership. But administrators, deans, and the university chancellor were totally unaware, according to the investigation.

That began to change in August 2011, when the Raleigh News & Observer began reporting on irregularities

Why Nyang'oro and Crowder did it

The investigation is highly critical of Crowder, who is described as the mastermind and main actor behind the fraud. But it argues that she had benevolent motives, as did other staff at the university who steered students into fraudulent classes.

Crowder, as the investigation tells it, was guilty of caring too much. Once a struggling student at UNC-Chapel Hill herself, she felt the college should be more inclusive of students who weren't the "best and the brightest." She was also known as a devoted fan of college sports.

he told the investigators he had more benevolent motivations

"These two passions — her desire to help underprepared students and her love of Chapel Hill athletics — would ultimately lead her to cut corners to help students and student-athletes make their grades," the investigators wrote.

Nyang'oro's light oversight of the department enabled Crowder's plans — and the report attributes the neglect to his need to his own travel and consulting schedule.

But he told the investigators he had more benevolent motivations. After two athletes he taught were forced to leave UNC due to poor grades, one was murdered. The other was arrested and ended up in jail. Nyang'oro "committed himself to preventing such tragedies in the future and to helping other struggling student-athletes to stay in school," investigators wrote.

What happens next at UNC

One key revelation in Wednesday's report was that the athletics department was tied to what had previously been considered an academic scandal. That raises the possibility that the NCAA could sanction the university's athletics programs.

Both Crowder and Nyang'oro have retired, and neither will face criminal charges. The Daily Tar Heel, UNC's student newspaper, reported Thursday that nine people will face disciplinary action as a result of Wainstein's report. All of them knew, or should have known, about the paper classes, according to the university.

Since 2011, the three investigations into the academic fraud have produced a slew of recommendations and reforms, many of which have been adopted. Those include random checks by university administrators to make sure lecture classes are actually meeting, new standards for admitting athletes, stricter reviews for faculty leadership, a new student records system, and new limitations on independent study credits.

"This should never have been allowed to happen," the university's chancellor, Carol Folt, said Wednesday. "At the same time, I want to underscore that there is a clear distinction between the 'then' and the 'now.' "

Correction: A previous version of this article misspelled Carol Folt's last name.