(CNN) Rick Singer called up his client, the wealthy parent of a college student, and went into his prepared lines.

The IRS was auditing his foundation, he said on the phone, and had some questions about payments the parent had made.

Singer was definitely not going to tell the IRS that the money was actually for cheating on the SATs or ACTs, he said. Nor would he mention that the parent's money truly went toward bribing college coaches in order to falsely get their children into elite universities. Instead, he would tell them the money was for charity. Sound good?

"Perfect. Got it," one parent responded.

"Of course," another parent told him.

"I think that's the --- the proper tact, for sure," a different parent said.

In fact, there was no active IRS audit. Each call to a parent was a set-up, made by Singer at the direction of law enforcement agents and recorded to further implicate them in the largest college admissions scam ever prosecuted in the US.

William "Rick" Singer, the mastermind of the college admissions scam, pleaded guilty to racketeering and conspiracy charges in federal court last week.

Singer, facing a mountain of evidence against him, had begun cooperating with federal investigators in September 2018.

As part of his cooperation, Singer made 20 such calls to clients at the direction of law enforcement from October 23 to 27, according to the criminal complaint, a veritable sting-a-thon operation that gifted prosecutors confirmation of the parents' knowledge of the scam.

The operation continued until March 3. In total, Singer made 34 calls to clients at the direction of law enforcement, and many others without their direction. On March 12, prosecutors announced that a total of 50 people had been arrested in the extensive scheme, including 33 wealthy parents

What the parents said

The criminal complaint against those parents includes transcripts of these recorded phone calls that can border on absurdist comedy . Many freely admitted to knowledge of the scam, and some even said that they had used that charitable donation as a write-off on their taxes.

In one November 29 call, Singer told Agustin Huneeus, a Napa vineyard owner, that he was not going to tell the IRS about Huneeus' $50,000 payment to cheat on his daughter's SATs. Singer said he wanted to make sure they were on the same page and that the money went to underserved kids, the complaint states.

"Dude, dude, what do you think, I'm a moron?" Huneeus said, according to the complaint.

"I got it, [Rick ]-- I got it," he allegedly added. "I'm going to say that I've been inspired how you're helping underprivileged kids get into college. Totally got it."

Huneeus has been charged with conspiracy to commit mail fraud and honest services mail fraud and is due in court March 29. CNN has reached out to Huneeus for comment.

Or consider the quotes in an October 24 recorded phone call with Marci Palatella, the CEO of a liquor distribution company. Singer reminded her that she had paid $75,000 to cheat on the SATs and more than $400,000 to falsely get her son into USC.

They then agreed to get on the same page and say that the money was for charity, according to the complaint.

"I mean, I love the work you're doing, and love the fact that you help take care of these kids and inspire them and go out into the communities," Palatella said, according to a transcript in the complaint

"It was a year we could afford to do it. That's -- which is not even true, but -- (laughs). We made sure it was."

Palatella has been charged with conspiracy and is due in court March 29, the Justice Department said. CNN has reached out to her for comment.

Flaws in the plan

However, using someone with Singer's checkered history as the focal point of these sting phone calls did not always go smoothly.

Singer pleaded guilty to charges of racketeering, money laundering conspiracy and conspiracy to defraud the United States in federal court in Boston last week. He also pleaded guilty to obstruction of justice.

That latter charge came in October -- a month after he began cooperating with investigators -- because he warned several of his clients that if they received a phone call from him it would most likely be recorded.

Singer admitted during his court hearing that he told the father of one prospective candidate he was wearing a wire and that they shouldn't say anything illegal.

"You haven't done anything wrong yet so please don't say anything that would be harmful to you guys because you haven't done anything, which was absolutely illegal," Singer said.

Singer obstructed justice with at least six families who had either taken part in the scam or were planning to do it, prosecutors said.

In addition, the transcripts show that some parents resisted speaking about the issue over the phone or otherwise caught on to the ruse.

In an October 25 call, Singer went into his usual lines about the IRS audit when Devin Sloane, the founder and CEO of a provider of drinking water and wastewater systems, cut him off.

"Wait [inaudible], wait," Sloane allegedly said, "let me ask you a question, shouldn't we get together for a coffee over this as opposed to over the phone?"

Singer responded "Whatever you want to do I'm fine." The complaint does not say whether or not they actually did meet up for coffee.

Sloane was charged with conspiracy to commit mail fraud and honest services mail fraud. CNN has reached out to Sloane for comment

Of the 34 calls made at the direction of law enforcement, the final one came on March 3, just a week before the charges were made public.

On that call, Singer told Stephen Semprevivo, a sales executive in Los Angeles, that Georgetown was looking into why students like Semprevivo's son who were not tennis players had been accepted as recruits.

After some discussion, the call disconnected. Semprevivo then called Singer back and said he was not comfortable talking about the issue, the complaint states. He then denied knowledge that his son was admitted through a scheme.

"You know, all I know is that we, you know, we used you for the charity stuff and we used you for the counseling, and your dealings are your dealings," Semprevivo said, according to the complaint.

Singer attempted to clarify the issue: "You don't agree that we got him in through tennis and you didn't know that [inaudible]?"

"I don't. I don't. I do-- you know, you did what you did, [Rick], and that was your stuff. Okay?" Semprevivo allegedly said.

Semprevivo was charged with conspiracy to commit mail fraud and honest services mail fraud. CNN has reached out to him for comment.