AUBURN, Alabama -- The NCAA did not find any major rules violations in Auburn's signing of quarterback Cam Newton and has concluded its investigation.

The NCAA enforcement staff also concluded its investigation into charges by four former players on HBO who accused the school of providing extra benefits. Again, it found no wrongdoing.

The NCAA issued a statement Wednesday saying it interviewed more than 50 people to see if Auburn provided Newton or his family improper benefits. The NCAA said it could not find any reason to keep the investigation open because its findings did not meet a "burden of proof" that Auburn did anything wrong in signing the quarterback who led the Tigers to the national title last season.

The NCAA said the investigation has to meet a higher standard "than rampant public speculation online and in the media.

The committee said it would review any additional information "if further investigation is warranted."

An additional 30 people were interviewed in the HBO investigation.

The NCAA, in a letter to the school, said the enforcement staff and Auburn reviewed "a number of allegations regarding the football program's compliance with NCAA legislation" over 13 months.

Four former players said on HBO -- Raven Gray, Stanley McClover, Chaz Ramsey and Troy Reddick -- that Auburn provided benefits. The NCAA said it could not substantiate the claims and wrote, in regard to Gray's charges were, in some instances, "disputed by others."

Auburn Athletics Director Jay Jacobs thanked the NCAA.

"We appreciate the NCAA and thank them for their professionalism and thoroughness during this exhaustive investigation. We are pleased to put this matter behind us," Jacobs said in a statement.

Here's the NCAA statement:

After conducting more than 80 interviews, the NCAA has concluded its investigation into Auburn University. The NCAA enforcement staff is committed to a fair and thorough investigative process. As such, any allegations of major rules violations must meet a burden of proof, which is a higher standard than rampant public speculation online and in the media. The allegations must be based on credible and persuasive information and includes a good-faith belief that the Committee on Infractions could make a finding. As with any case, should the enforcement staff become aware of additional credible information, it will review the information to determine whether further investigation is warranted.