The slew of criminal charges in the sweeping college cheating scam originated from an unrelated federal case in the Boston area — and a financial executive desperate for mercy, according to a new report.

The feds were tipped off to what would be the biggest college admissions scheme ever prosecuted thanks to the businessman, who was under investigation in a securities fraud case, the Wall Street Journal reported Wednesday.

In a bid for leniency, he told investigators that Rudolph “Rudy” Meredith, the head women’s soccer coach at Yale, solicited bribes from him in exchange for recommending his daughter for admission as an athletic recruit, a source told the Journal.

The probe turned to Meredith — then widened to nearly 50 others as the feds learned the scam involved wealthy parents, other college athletic coaches, and crooked SAT and ACT test proctors.

At the heart of the scheme was William “Rick” Singer, a college prep expert whose business in California was aimed at getting kids into some of the nation’s top schools.

On Tuesday, Singer pleaded guilty to charges that he accepted more than $25 million in bribes to help students cheat on their college entrance exams or gain acceptance to schools as athletes — even when they didn’t play sports.

Thirty-three parents are among those charged, including TV actresses Lori Loughlin and Felicity Huffman.