The investigation that has heaped scrutiny upon Harvard, sidelined the captains of the men’s basketball team, and landed nearly 2 percent of the student body in disciplinary hot water all began with a 1910 Congressional revolt and a simple typo.

In a letter dated May 14 obtained by The Crimson this week, assistant professor Matthew B. Platt described the series of discoveries that led him to bring the final take-home exams submitted by his students in Government 1310: “Introduction to Congress” to the attention of the Administrative Board, a move that launched Harvard’s most sweeping and public plagiarism inquiry in recent memory.

The letter, addressed to Ad Board Secretary John “Jay” L. Ellison, narrated Platt’s first suspicions of plagiarism in 13 exams among the 279 submitted in the spring course.

Platt’s initial report prompted the Ad Board to spend the summer reviewing all the final exams. By the time the College publicly announced the investigation on Aug. 30, the number of students under investigation had ballooned to about 125 undergraduates.

Platt’s letter identified two groups of students represented among the first 13 suspicious exams: graduating members of the Class of 2012 and members of the baseball team.

Members of the basketball and football teams have been implicated in the scandal, but no professor or administrator had previously linked any extracurricular organizations to the case.

In his letter, Platt said he had detected similar strings of words in multiple questions on multiple exams, including the same unusual responses, the same misunderstandings of course materials, and an identical typo.

On a bonus question, “all the answers use the same (incorrect) reading of the course material in arguments that are identically structured,” Platt wrote.

He wrote that one of his teaching fellows originally detected suspicious similarities on that question, which read, “Describe two developments in the history of Congress that ostensibly gave individual MCs [members of Congress] in the House greater freedom and/or control but ultimately centralized power in the hands of party leadership.”

Several students answered that question with the same two “somewhat obscure” responses—the Cannon Revolt of 1910 and longtime 19th century Congressman Henry Clay, Platt wrote.

Platt wrote that upon further examination, “comparisons with some of these exams also suggest that there was collaboration on the three other short answer questions and essays.”

Then he compared the suspicious exams with a random test selected from the class.

“I am convinced that the similarities between these papers are not the product of chance,” he concluded.

Also among the shared phrases were “Freddie Mac’s stealth lobbying campaign” and “22, 500 organizations in 2008,” Platt wrote. He also noted that the same typo—an unnecessary space in “22, 500”—was present in two exams.

Interim baseball coach Thomas Lo Ricco could not be reached for comment Tuesday night on the team’s mention in the letter, and team captain Kyle R. Larrow ’13 declined to comment.

Ellison declined to comment on the letter, saying it is a confidential Ad Board document—indeed, it is branded with a “CONFIDENTIAL” stamp.

Platt, who has declined to comment since the scandal first broke, did not respond to repeated requests for comment on Tuesday.

—Staff writer Mercer R. Cook can be reached at mcook@college.harvard.edu.

—Staff writer Rebecca D. Robbins can be reached at rrobbins@college.harvard.edu.