Joel Rubin, Matthew Ormseth, Suhauna Hussain and Richard Winton:

“Our first lead in this came during interviews with a target of an entirely separate investigation, who gave us a tip that this activity might be going on,” he said.

The tip led investigators to a soccer coach at Yale University, who, in turn, pointed them to William “Rick” Singer, the college admissions consultant who would confess to being the mastermind of the admissions racket. With Singer’s cooperation, FBI agents set about building cases against dozens of the wealthy parents on his client list as well as people at universities across the country Singer allegedly paid to help students cheat their way into school. Prosecutors needed less than a year from that first tip to file criminal charges, a remarkably quick turnaround for a case so large and with such high stakes.

In all, 50 people have been charged — including 33 parents, several college coaches, a man Singer paid to take college admission exams for students, and Singer himself, who pleaded guilty to several felonies in a deal with prosecutors. The investigation is ongoing, and prosecutors indicated in court last week that more people were likely to be charged.

Not included in the pool of defendants, however, is Tobin, whom multiple law enforcement officials and a person close to him identified as the unnamed tipster Lelling credited with setting the investigation in motion.