Since the mastermind of the college admissions scandal, William Singer, pleaded guilty last March to racketeering and other charges, he has been mostly offstage, paddleboarding and enjoying the California sun while many of his former clients head off to prison.

But this week, Mr. Singer, who admitted to organizing a scheme to cheat on tests and bribe college coaches to get students into elite schools, was again the center of attention. Lawyers for the actress Lori Loughlin and other parents said that notes Mr. Singer had taken while cooperating with federal investigators showed that they pushed him to lie to incriminate his clients.

They said that Mr. Singer’s own words suggested that parents did not knowingly engage in a conspiracy to bribe coaches, as prosecutors have argued, and they accused prosecutors of sitting on the evidence for months in violation of their legal obligations.

“Loud and abrasive call with agents,” Mr. Singer wrote on Oct. 2, 2018, in a note with several typos and misspellings. “They continue to ask me to tell a fib and not restate what I told my clients as to where there money was going - to the program not the coach and that it was a donation and they want it to be a payment.”